Chapter IV: Appendix: 574 (3)

Order 1. =Characeæ.= Algæ with a peculiar odour, often incrusted with lime, and of a brittle nature. They generally grow gregariously in large masses at the bottom of fresh and brackish water, and are from a few inches to more than a foot in height. The stem has long internodes which in _Nitella_ are formed of one cylindrical cell; in _Chara_ of a similar cell, but closely surrounded by a cortical layer of smaller ones. The protoplasm in contact with the cell-wall exhibits in a well-marked degree the movement of rotation (cyclosis), carrying the chlorophyll corpuscles along with it. The internodes are separated from each other by a layer of small cells (nodal cells) from which the leaves are produced. The leaves are borne in whorls of from 5–12 which regularly alternate with one another as in the higher verticillate plants; a branch is borne in the axil of the first formed leaf of each whorl (Fig. 61 _A_, _n_).

The leaves are constructed in the same manner as the stem; they are divided into a series of joints, but have only a limited power of growth; their terminal cell, too, is not enclosed by a cortex. Leaflets are borne at their nodes. The growth of the stem is unlimited, and proceeds by means of an apical cell (Fig. 62 _s_). The apical cell divides into a segment-cell and a new apical cell. The segment-cell then divides by a transverse wall into two cells, one lying above the other; the lower one, without any further division, becomes one of the long, cylindrical, internodal cells (Fig. 62 _in_), and the upper one (Fig. 62 _n_) divides by vertical walls to form the nodal cells. The cortical cells (Fig. 62 _r_) which surround the long internodal cells of _Chara_, are derived from the divisions of the nodal cells; the cells covering the upper portion of an internodal cell being derived from the node immediately above it, and those in the lower part of the internode from the node below it.

The organs of reproduction are very conspicuous by their colour and form. They are always situated on the leaves, the plants being very frequently monœcious. The antheridia (Fig. 61 _B_, _a_) are modified leaflets or the terminal cell of a leaf; they are spherical and become red when mature. Their wall consists of 8 “shields,” _i.e._ of plate-like cells, 4 of which cover the upper half, and are triangular; the 4 round the lower half, to which the stalk of the antheridia is attached, being quadrilateral, with sides of unequal length. The shields (Fig. 61 _C_) have dentated edges, with the teeth fitting into one another, and their faces ornamented with ridges. From the centre of the internal face of each shield (_C_) a cylindrical cell, the _manubrium_, projects nearly as far as the centre of the antheridium; at the inner end of each of the manubria a spherical cell, the _capitulum_, is situated. Each capitulum bears six secondary capitula, from each of which four long coiled filaments (_C_, _D_) project into the cavity of the antheridium. These filaments are divided by transverse walls into from 100–200 discoid cells, in each of which a biciliated, coiled spermatozoid is developed (_D_, _E_) from the nucleus. The spermatozoids escape from their mother-cell and are set free by the shields separating from one other.

The female organ of reproduction (Fig. 61 _B_, 63) is a small modified shoot, whose apical cell functions as an oogonium, its protoplasm forming the oosphere, which has a colourless receptive-spot at the summit (Fig. 63 _u_). The oogonium is situated on a nodal cell, from which 5 cells grow out in a circle and coil round the oogonium, covering it with a close investment. These cells divide once or twice at the top, so that 5 or 10 small cells are cut off, which project above the oogonium and form the so-called “crown” (Fig. 63 _k_). The crown either drops off at fertilisation, or its cells separate to form a central canal for the passage of the spermatozoids. The wall of the oosphere[9] above the receptive spot becomes mucilaginous, and allows the spermatozoid to fuse with the oosphere. The oospore, on germination (Fig. 64 _sp_), becomes a small filamentous plant of limited growth (Fig. 64 _i_, _d_, _q_, _pl_)--the proembryo--and from this, as a lateral outgrowth, the sexual generation is produced.

The order is divided into two sub-orders:--

A. NITELLEÆ. The crown consists of 10 cells; cortex absent: _Nitella_, _Tolypella_.

B. CHAREÆ. The crown consists of 5 cells; cortex present: _Tolypellopsis_, _Lamprothamnus_, _Lychnothamnus_, _Chara_.

_Chara crinita_ is parthenogenetic; in large districts of Europe only female plants are found, yet oospheres are formed capable of germination.

About 40 species of fossilized _Chara_, determined by their carpogonia, are known in the geological formations from the Trias up to the present day.

Class 8. =Phæophyceæ (Olive-Brown Seaweeds).=

The Phæophyceæ are Algæ, with chromatophores in which the chlorophyll is masked by a brown colour (phycophæin). The product of assimilation is a carbohydrate (fucosan), _never true starch_. In the highest forms (_Fucaceæ_), the thallus presents differentiation into stem, leaf, and root-like structures. The asexual reproduction takes place by means of zoospores. The sexual reproduction is effected by the coalescence of motile gametes, or by oogamous fertilisation. The swarm-cells are _monosymmetric_, each moved by two cilia which are true protoplasmic structures, and generally _attached laterally_ (Fig. 65). The Phæophyceæ are almost entirely saltwater forms; a few species of _Lithoderma_ live in fresh water.

The class is divided into two families:--

1. PHÆOSPOREÆ: 1 Sub-Family, Zoogonicæ; 2 Sub-Family, Acinetæ.

2. CYCLOSPOREÆ: Fucaceæ.

Family 1. =Phæosporeæ.=

The family consists of multicellular plants, whose cells are firmly united together to form a thallus; this, in the simplest cases, may be a branched filament of cells (_Ectocarpus_), or, in the highest, may resemble a stem with leaves (_Laminariaceæ_), while all transitional forms may be found between these two. The thallus grows by intercalary divisions (_e.g. Ectocarpus_), or by an apical cell (_e.g._ _Sphacelaria_); pseudo-parenchymatous tissue may sometimes be formed by cells, which were originally distinct, becoming united together. The size of the thallus varies; in some species it is quite small--almost microscopical,--while in the largest it is many metres in length.

The vegetative cells in the lower forms are nearly uniform, but in those which are more highly developed (_Laminariaceæ_ and _Fucaceæ_), they are sometimes so highly differentiated that mechanical, assimilating, storing and conducting systems may be found; the last named systems are formed of long cells with perforated, transverse walls, which bear a strong resemblance to the sieve-tubes in the higher plants.

The colouring matter in the living cells (“phæophyl”) contains chlorophyll; but this is concealed by a brown (“phycophæin”), and a yellow (“phycoxanthin”) colouring material, and hence all these Algæ are a lighter or darker _yellow-brown_. Starch is not formed. Asexual reproduction takes place, (1) by zoospores which arise in unilocular zoosporangia, and are monosymmetric, with two cilia attached laterally at the base of the colourless anterior end (Fig. 65), the longer one being directed forwards and the shorter backwards; or (2) by aplanospores (?).

Sexual reproduction has only been discovered in a few cases, and takes place by means of gametes (oogamous fertilisation perhaps occurs in the Tilopteridæ). The gametes have the same structure as the zoospores, and arise in multilocular gametangia; these, like the zoosporangia, are outgrowths from the external surface, or arise as modifications from it. The conjugating gametes may be similar (_e.g. Ectocarpus pusillus_), or there may be a more or less pronounced difference of sex, an indication of which is found in _Ectocarpus siliculosus_ (Fig. 66). When the gametes in this species have swarmed for a time, some, which are generally larger, are seen to attach themselves by one of the cilia, which by degrees is shortened to form a kind of stalk (compare the upper gamete in Fig. 66 _II_); these are the female gametes, which now become surrounded by a number of males endeavouring to conjugate with them, but only one succeeds in effecting fertilisation. The protoplasm of the two gametes coalesces (Fig. 66 _III_), and a zygote (_e_) is formed. The male gametes which do not conjugate may germinate, but the plants derived from them are much weaker than those produced by the zygotes. Strongly pronounced sexual differences are found in the Cutleriaceæ, in which order the male and female gametes arise in separate gametangia (Fig. 67 _A_). The male gametes (Fig. 67 _D_) are much smaller than the female gamete (Fig. 67 _C_); the latter, after swarming for a short time, withdraws the cilia, and is then ready to become fertilised (Fig. 67 _B_, _E_), thus we have here a distinct transition to the oogamous fertilisation which is found in the Fucaceæ. Alternation of generations is rarely found.

1. Sub-Family. =Zoogonicæ.=

Reproduction by means of gametes and zoospores.

Order 1. =Ectocarpaceæ.= The thallus consists of single or branched filaments with intercalary growth, extending vertically from a horizontal, branched filament or a disc, but sometimes it is reduced to this basal portion only. Zoosporangia and gametangia (for fertilisation see Fig. 66) are either outgrowths or arise by the transformation of one or several of the ordinary cells. The most common genera are: _Ectocarpus_ and _Pylaiella_.

Order 2. =Choristocarpaceæ.= _Choristocarpus_, _Discosporangium_.

Order 3. =Sphacelariaceæ.= The thallus consists of small, parenchymatous, more or less ramified shoots, presenting a feather-like appearance. In the shoots, which grow by means of an apical cell (Fig. 68 _S_), a cortical layer, surrounding a row of central cells, is present. Sporangia and gametangia are outgrowths from the main stem or its branches. _Sphacelaria_, _Chætopteris_ are common forms.

Order 4. =Encoeliaceæ.= _Punctaria_, _Asperococcus_, _Phyllitis fascia_.

Order 5. =Striariaceæ.= _Striaria_, _Phlœospora_.

Order 6. =Dictyosiphonaceæ.= _Dictyosiphon._

Order 7. =Desmarestiaceæ.= _Desmarestia aculeata_ is common.

Order 8. =Myriotrichiaceæ.= _Myriotrichia._

Order 9. =Elachistaceæ.= _Elachista fucicola_ is a common epiphyte on species of _Fucus_.

Order 10. =Chordariaceæ.= The shoot-systems are often surrounded by mucilage. _Chordaria_; _Leathesia difformis_ occurs as rounded, brown-green masses of the size of a nut, generally attached to other Seaweeds.

Order 11. =Stilophoraceæ.= _Stilophora rhizodes_ is common.

Order 12. =Spermatochnaceæ.= _Spermatochnus paradoxus_ is common.

Order 13. =Sporochnaceæ.= _Sporochnus._

Order 14. =Ralfsiaceæ.= _Ralfsia verrucosa_ is common as a red-brown incrustation on stones and rocks at the water’s edge.

Order 15. =Lithodermataceæ.= Some species of the genus _Lithoderma_ occur in fresh water.

Order 16. =Laminariaceæ.= The thallus is more or less leathery, and has generally a root-like lower part (Fig. 69) which serves to attach it, and a stalk or stem-like part, terminated by a large leaf-like expansion. Meristematic cells are situated at the base of the leaf, and from these the new leaves are derived. The older leaf thus pushed away by the intercalary formation of the younger ones, soon withers (Fig. 69). Gametes are wanting. Zoosporangia are developed from the lower part of a simple, few-celled sporangiophore, which is an outgrowth from a surface-cell and has a large club-formed apical cell. The sporangia are aggregated into closely packed sori, which cover the lower part of the terminal leaf, or occur on special, smaller, lateral, fertile fronds (_Alaria_). Most of the species belonging to this order live in seas of moderate or cold temperature and occur in the most northern regions that have yet been explored, forming their organs of reproduction during the cold and darkness of the arctic night. _Laminaria_ is destitute of a midrib and has only one terminal leaf. _L. digitata_ has a broad leaf, which, by the violence of the waves, is torn into a number of palmate strips (Fig. 69). _L. saccharina_ has a small, undivided leaf. _Alaria_ has a midrib and special fertile fronds. _A. esculenta_ occurs plentifully on the west coast of Norway and on the shores of Great Britain. _Chorda filum_, a common seaweed, is thick, unbranched, and attains a length of several metres, without any strong demarcation between stalk and leaf. Some attain quite a gigantic size, _e.g. Macrocystis pyrifera_, whose thallus is said sometimes to be more than 300 metres in length. The _Lessonia_-species, like the above, form submarine forests of seaweed on the south and south-west coasts of South America, the Cape, and other localities in the Southern Hemisphere.

USES. The large Laminarias, where they occur in great numbers,
are, like the Fuci, used for various purposes, for example, in
the production of iodine and soda, and as an article of food
(_Laminaria saccharina_, _Alaria esculenta_, etc.). _Laminaria
saccharina_ contains a large quantity of sugar (mannit) and is
in some districts used in the preparation of a kind of syrup;
in surgical operations it is employed for the distension of
apertures and passages, as for instance the ear-passage. It
is by reason of the anatomical peculiarities and structure of
the cell-walls, that they are employed for this purpose. The
cell-walls are divided into two layers, an inner one which
has very little power of swelling, and an outer one, well
developed and almost gelatinous--the so-called “intercellular
substance”--which shrivels up when dried, but can absorb water
and swell to about five times its size. The stalks of _Laminaria
clustoni_ are officinal.

Order 17. =Cutleriaceæ.= The thallus is formed by the union of the originally free, band-shaped shoots. The growth is intercalary. Sexual reproduction by the conjugation of male and female gametes. An asexual generation of different appearance, which produces zoospores, arises from the germination of the zygote. _Cutleria_, _Zanardinia_.

Sub-Family 2. =Acinetæ.=

Branched, simple cell-rows with intercalary growth. The organs of reproduction are partly uni-and partly multicellular; in the unicellular ones a cell without cilia is formed, which may be destitute of a cell-wall, but has one nucleus (oosphere?), or which has a cell-wall and contains several (generally four) nuclei (aplanospores?); in the multicellular, monosymmetric swarm-cells with two cilia (spermatozoids?) are formed. The fertilisation has not been observed.

Order 1. =Tilopteridaceæ.= _Haplospora_, _Tilopteris_.

Family 2. =Cyclosporeæ.=

The individuals are multicellular, with growth by an apical cell. The thallus--often bilateral--is differentiated into a root-like structure (attachment-disc), and stem, sometimes also into leaves (_Sargassum_). Sometimes a differentiation occurs into various tissue-systems, viz. an external assimilating tissue, a storing tissue, a mechanical tissue of thickened, longitudinal, parenchymatous, strengthening cells, and a conducting tissue of sieve-cells, or of short sieve-tubes with perforated walls. Colouring material, as in Phæosporeæ. Vegetative reproduction can only take place by means of detached portions of the thallus (_Sargassum_), which are kept floating by means of bladders (Fig. 70 _A_, _a_, Fig. 72). Zoospores are wanting.

The sexual reproduction takes place by oogamous fertilisation. The oogonia and antheridia are formed inside special organs (conceptacles), and are surrounded by paraphyses. The conceptacles (Fig. 70 _B_, Fig. 71 _b_) are small, pear-shaped or spherical depressions, produced by a special ingrowth of the surface cells of the thallus, and their mouths (_ostioles_) project like small warts; they are either situated near the end of the ordinary branches of the thallus (_Fucus serratus_, Fig. 71 _a_) which may be swollen on this account (_Fucus vesiculosus_, Fig. 70 _A_, _b_), or on special short branches (_Ascophyllum_, _Sargassum_). The vertical section of a conceptacle is seen in Fig. 70 _B_ (see also Fig. 71 _b_) where, in addition to the paraphyses, oogonia only are seen (_F. vesiculosus_ is diœcious--male plant, yellow-brown; female plant, olive-brown); but in some species antheridia, together with oogonia, are produced in the same conceptacle. The oogonia are large, almost spherical cells, situated on a short stalk, in each of which are formed from 1–8 (in _Fucus_, 8; in _Ascophyllum_, 4; in _Halidrys_, 1; in _Pelvetia_, 2) rounded, immotile oospheres. The wall of the oogonium ruptures, and the oospheres, still enclosed in the inner membrane, are ejected through the mouth of the conceptacle, and float about in the water, being finally set free by the bursting of the inner membrane. The antheridia are oblong cells (Fig. 70 _C_, _a_), many of which are produced on the same branched antheridiophore (Fig. 70 _C_); the numerous spermatozoids are provided with 2 cilia and are very small (Fig. 70 _D_, two antheridia surrounded by spermatozoids, one being open). The spermatozoids, still enclosed by the inner membrane of the antheridium, are similarly set free, and fertilisation takes place in the water, numerous spermatozoids collecting round the oosphere (Fig. 70 _E_), which is many times larger, and by their own motion causing it to rotate. After fertilisation, the oospore surrounds itself with a cell-wall and germinates immediately, attaching itself (Fig. 70 _F_) to some object, and by cell-division grows into a new plant.

Order 1. =Fucaceæ.= The following species are common on our coasts: _Fucus vesiculosus_ (Fig. 70) has a thallus with an entire margin, and with bladders arranged in pairs; _F. serratus_ (Fig. 71) without bladders, but with serrated margin; _Ascophyllum nodosum_ has strap-like shoots, which here and there are swollen to form bladders; _Halidrys siliquosa_ has its swimming bladders divided by transverse walls; _Himanthalia lorea_, which is found on the west coast of Norway, and the south coast of England, has a small perennial, button-shaped part, from the centre of which proceeds the long and sparsely branched, strap-like, annual shoot, which bears the conceptacles. The Gulf-weed (_Sargassum bacciferum_, Fig. 72) is well known historically from the voyage of Columbus; it is met with in large, floating, detached masses in all oceans, and is found most abundantly in the Atlantic, off the Canary Islands and the Azores, and towards the Bermudas. The stalked, spherical air-bladders are the characteristic feature of this genus. The thallus is more highly developed than in _Fucus_, and there is a contrast between the stem and leaf-like parts. The portions which are found floating are always barren, only those attached are fertile.

USES. The Fucaceæ, like the Laminariaceæ, are used as manure
(the best kinds being _Fucus vesiculosus_ and _Ascophyllum
nodosum_), for burning to produce kelp, and as food for domestic
animals (_Ascophyllum nodosum_ is especially used for this
purpose).

Class 9. =Dictyotales.=

The plants in this class are multicellular, and brown, with apical growth, new cells being derived either from a flat apical cell, or from a border of apical cells. The thallus is flat, leaf- or strap-shaped, attached by haptera, which are either found only at the base, or on the whole of the lower expansion of the thallus. The cells are differentiated into the following systems of tissues: an external, small-celled layer of assimilating cells, generally one cell in thickness, and an internal, large-celled layer of one or only a few cells in thickness, forming the mechanical and conducting tissues. All the reproductive cells are motionless. Asexual reproduction by naked, motionless spores (tetraspores) which are formed 1–4 in each tetrasporangium, the latter being outgrowths from the surface cells of special, sexless individuals. Zoospores are wanting. The sexual organs are of two kinds, oogonia and antheridia, which are formed from the surface cells, either on the same or different individuals. The oogonia are spherical or oval, and are generally placed close together; each contains one oosphere, which on maturity is ejected into the surrounding water, and is then naked and motionless. The antheridia are formed of longitudinal cells, united in groups, whose contents by repeated divisions--transverse and longitudinal--are divided into a large number of small, colourless, motionless spermatia--round or elongated--which are set free by the dissolution of the wall of the antheridium. The process of fertilisation has not yet been observed.

The Dictyotales, in having tetraspores and spermatia, deviate considerably from the Phæophyceæ, but may be classed near to the Tilopteridæ, in which there are asexual spores with 4 cell-nuclei, which may be considered as an indication of the formation of tetraspores.

Order 1. =Dictyotaceæ.= _Dictyota dichotoma_ which has a thin,
regularly dichotomously divided thallus, occurs on the coasts of
the British Isles. _Padina_ is found on the south coast.

Class 10. =Rhodophyceæ (Red Seaweeds).=

The plants comprised in this class are multicellular; they are simple or branched filaments, or expansions consisting of 1 to several layers of cells; the thallus may be differentiated (as in many _Florideæ_), to resemble stem, root, and leaf. The cells contain a distinctly differentiated nucleus (sometimes several), and distinct chromatophores, coloured by rhodophyll. The chlorophyll of the chromatophores is generally masked by a red colouring matter (phycoerythrin), which may be extracted in cold, fresh water; or rarely by phycocyan. Pyrenoids occur in some. Starch is never formed in the chromatophores themselves, but a modification--Florideæ starch--may be found in the colourless protoplasm. Asexual reproduction by motile or motionless spores (tetraspores) which are devoid of cilia and of cell-wall. Swarmspores are never found.

Sexual reproduction is wanting, or takes place by the coalescence of a spermatium and a more or less developed female cell. The spermatia are naked masses of protoplasm, devoid of cilia and chromatophores. The female cell (carpogonium) is enclosed by a cell-wall, and after fertilisation forms a number of spores, either with or without cell-walls (carpospores), which grow into new individuals.

The Rhodophyceæ may be divided into two families:

1. BANGIOIDEÆ.
2. FLORIDEÆ.

Family 1. =Bangioideæ.=

The thallus consists of a branched or unbranched cell-filament, formed of a single row or of many rows of cells, or of an expansion, one or two layers of cells in thickness, but without conspicuous pores for the intercommunication of the cells. The growth of the thallus is chiefly intercalary. The star-like chromatophores contain chlorophyll and are coloured blue-green with phycocyan, or reddish with phycoerythrin; all these colouring matters are occasionally found in the same cell (_Bangia_-species). Asexual reproduction by tetraspores, without cilia, but capable of amœboid movements.

Sexual reproduction is wanting, or takes place by the coalescence of a spermatium with a carpogonium, which is only slightly differentiated from the vegetative cells, and is devoid of a trichogyne. The carpospores are destitute of cell-wall and arise directly by the division of the fertilised oosphere. The Bangioideæ occur chiefly in salt water.

Order 1. =Goniotrichaceæ.=--The thallus consists of a
branched cell-filament without rhizoids. Tetraspores are
formed directly from the entire contents of the mother-cell,
without any preceding division. Fertilisation unknown.
_Asterocystis_, _Goniotrichum_.

The _Goniotrichaceæ_, through the blue-green _Asterocystis_,
are allied to the Myxophyceæ, and through _Goniotrichum_ to the
_Porphyraceæ_.

Order 2. =Porphyraceæ.=--The thallus is formed of an expansion
consisting of a layer of 1–2 cells, which, at the base, are
attached to the substratum by means of a special form of haptera
(_Porphyra_, _Diploderma_); or of unbranched (very rarely
slightly branched) filaments, attached at the base by haptera
(_Bangia_): or it extends from a prostrate cell-disc (various
species of _Erythrotrichia_). Tetraspores are formed after one
or more divisions of the mother-cell, either from the whole or
only a part of its contents; they possess amœboid movements,
or have a jerky, sliding-forward motion. The antheridia have
the same appearance as the vegetative cells, but divide several
times, and several spermatia are formed, either simultaneously
from the whole contents (_Porphyra_, _Bangia_), or the spermatia
are successively formed from a part of the contents of the
antheridium (_Erythrotrichia_). The carpogonium is without a
trichogyne, but the oosphere has a colourless spot which may
sometimes rise a little above the surface of the thallus, and
may be considered as an early stage in the development of the
trichogyne. The spermatia form a canal through the membrane of
the carpogonium, and their contents coalesce with the oosphere
at its colourless spot. The fertilised oosphere divides on
germination into a number of carpospores, which are set free as
naked, motionless masses of protoplasm, which grow and give rise
to new individuals (alternation of generations).

Family 2. =Florideæ.=

The thallus has one or more apical cells, grows principally by apical growth, and may be differentiated into root, stem, and leaf. The chromatophores vary in form, but have a red or brownish colour, due to chlorophyll and phycoerythrin. Asexual reproduction by motionless tetraspores, which generally arise by the division into four of the contents of the tetrasporangium. The carpogonium has a trichogyne, and the carpospores, which are formed indirectly from the fertilised oosphere, possess a cell-wall.

The thallus may assume very different forms. In the simplest species it is filamentous and formed of single, branched rows of cells (_Callithamnion_, etc., Fig. 73). _Ceramium_ has a filamentous thallus, generally dichotomously forked (Fig. 75), or sometimes pinnately branched, which, at the nodes, or throughout its entire length, is covered by a layer of small cortical cells. _Polysiphonia_ (Fig. 74) has a filamentous, much branched thallus, made up of a central cylindrical cell, surrounded by a layer of other cells, cortical cells, which in length and position correspond to the central ones. In many of the Red Algæ the vegetative organs are differentiated into stems and leaves, the former having, as in _Chara_, unlimited growth in length, whilst the latter soon attain their full development. _Chondrus_ has a fleshy, gelatinous thallus, without nodes; it is repeatedly forked into flat branches of varying thickness. _Furcellaria_ has a forked thallus with thick branches and without nodes. The thallus of _Delesseria_ (Fig. 76) consists of branches, often bearing leaf-like structures, with a midrib and lateral ribs springing from it. These ribs persist through the winter, and at the commencement of the succeeding period of vegetation the lateral ribs become the starting points for new leaves. In _Corallina_ the thallus is pinnately branched, and divided into nodes and internodes. The name has been given to this genus from the fact that the thallus is incrusted with carbonate of lime to such a degree that it becomes very hard, and the whole plant adopts a coral-like appearance. Other genera which are similarly incrusted, and have a leaf-like or even crustaceous thallus (such as _Melobesia_, _Lithothamnion_), are included in this family.

In some instances the cells of the thallus may be found _differentiated_ into more or less well defined tissues, so that it is possible to find special assimilating, mechanical, and conducting tissues, the last named in some cases having the double function of conducting and of serving as a reservoir in which starch is found as a reserve material. The cells of the Florideæ, which are formed by the division of a mother-cell into two daughter-cells of unequal size, have always larger or smaller pits in the cell-walls, and the thin cell-wall separating two pits from each other is perforated by a number of small holes. These pits are particularly developed in the conducting tissues, but sieve-tubes are very rarely to be found.

_Tetraspores_ may be wanting (_e.g. Lemanea_) or may often arise on special, non-sexual individuals. In some (_e.g. Batrachospermum_) only one tetraspore is formed in each tetrasporangium, but the number is generally four, which may be formed tetrahedrally (Fig. 73) or by divisional walls perpendicular to each other, or even in a single row. The tetrasporangia in some species are free (Fig. 73), but in the majority they are embedded in the thallus.

The sexual reproduction (discovered by Thuret and Bornet, 1867) differs in the essential points from that of all other plants, and approaches most nearly to the sexual reproduction of the _Bangioideæ_. The sexual cells are developed from the terminal cells (never nodal cells) of the branched cell-filaments, which constitute the thallus. The mother-cells of the spermatia (_spermatangia_) are generally arranged in a group, in the so-called _antheridia_ (Figs. 74, 77 _A_, _a_). On becoming ripe the membrane of the spermatangium ruptures and the _spermatia_ emerge as spherical or ovoid, naked (a little later they may possess a cell-wall) masses of protoplasm which are not endowed with the power of motion, and hence are carried passively by the current of the water in which they may happen to be, to the female cell. This latter is analogous with the oogonium of the Green Algæ. The female reproductive organ is termed the _procarpium_, and consists of two parts, a lower swollen portion--the _carpogonium_ (Fig. 77 _b_ in _A_ and _B_)--which contains the cell-nucleus, and an upper filamentous prolongation--the _trichogyne_ (Fig. 77 _B_)--which is homologous with the colourless receptive spot of the oosphere of the Green Algæ, and the _Porphyraceæ_. In the sexual reproduction of the majority of the Florideæ, a very important part is played by certain special cells, rich in cell-contents--the _auxiliary cells_. These are either dispersed in the interior of the thallus, or are arranged together in pairs with the cell-filament which bears the carpogonium, and are generally united with this to form an independent multicellular _procarpium_. The spermatia attach themselves firmly to the trichogyne and surround themselves with a cell-wall. The dividing wall at the point of contact is perforated, and the nucleus of the spermatium probably travels through the trichogyne to the swollen part of the procarpium--the _carpogonium_--and fuses with its nucleus. After fertilisation the trichogyne withers (Fig. 77 _C_), but the lower portion of the procarpium, constituting the _fertilised oosphere_, grows out and forms in various ways, first a tuft of spore-forming filaments known as _gonimoblasts_, and finally the _carpospores_. These latter form a new asexual generation (compare the germination of the oospore of _Œdogonium_ and _Coleochæte_).

The gonimoblasts may arise in three ways:--

1. In the _Nemalionales_, branched filaments grow out from the
oosphere and form an upright, compressed or expanded tuft of
spore-forming filaments.

2. In the _Cryptonemiales_, several branched or unbranched
filaments (_ooblastema-filaments_) grow out from the oosphere,
and conjugate in various ways with the auxiliary cells. The
gonimoblasts are then formed from the single cells produced by
the conjugation.

3. In the _Gigartinales_ and _Rhodymeniales_ the oosphere
conjugates with an auxiliary cell by means of a short
ooblastema-filament, and from this auxiliary cell a gonimoblast
is produced.

The motionless _carpospores_, which sometimes in the early
stages are naked, and afterwards invested with a cell-wall, are
developed from the terminal cells (and perhaps also from some
of the other cells) of the branches of the gonimoblast. The
gonimoblasts constitute sharply defined parts of the plant in
which the carpospores arise. These parts are called _cystocarps_
and are either naked (Fig. 77 _E_), or surrounded by a covering
(pericarp or involucre, Fig. 77 _A_) formed in different
ways. On this account the Florideæ were formerly divided into
GYMNOSPOREÆ (_Batrachospermum_, _Nemalion_, _Ceramium_, etc.)
and ANGIOSPOREÆ (_Farcellaria_, _Lejolisia_, _Delesseria_,
_Melobesia_, etc.).

The Florideæ are divided into four sub-families:--

Sub-Family 1. =Nemalionales.= The fertilised oosphere produces
directly the gonimoblast.

Order 1. =Lemaneaceæ.= Algæ of brownish colour and living in
fresh water. They lack tetraspores, and the very sparingly
branched fertile filaments, composed of many rows of cells, grow
out from a proembryo, which consists of a single row of cells
bearing branches. _Lemanea fluviatilis_, often found on rocks
and stones in quickly flowing streams.

Order 2. =Helminthocladiaceæ.= Tetraspores are generally wanting
(_e.g._ in _Nemalion_) or arise one in each tetrasporangium
(_e.g. Batrachospermum_) and it is only in _Liagora_
that four cruciate tetraspores are formed. _Chantransia
corymbifera_ consists of simple, branched cell-rows, and is
an independent species. Several other _Chantransia-forms_,
living in fresh water, are “proembryos” of species of the genus
_Batrachospermum_. The germinating carpospore grows out into
filaments and forms a so-called proembryo which, if not shaded,
attains only a small size, but when growing in shady situations
presents a much greater development. These highly developed
proembryos have been described as species of _Chantransia_.
The proembryo can reproduce by division, or by tetraspores
which are developed singly in the sporangia; in _B. vagum_ and
_B. sporulans_ which do not possess fully developed female
reproductive organs, the proembryos serve almost entirely to
reproduce the species. The young _Batrachospermum_-plant arises
from the end of an upright filament of the proembryo. The
proembryo is generally persistent, and continually produces new
_Batrachospermums_. These latter bear the sexual reproductive
organs and also whorls of branches: the central row of cells
is enclosed by cells growing from the base of the whorls of
branches, and from these cortical cells secondary proembryos
are developed. In this alternation of shoots there is really
no alternation of generations, since the proembryo and the
shoots with the sexual reproductive organs are parts of the same
thallus.

Several species of _Batrachospermum_ have a bluish green or
verdigris colour. _Nemalion multifidum_ has a brown-red thallus,
slightly branched, which is attached to rocks near the water’s
edge.

Order 3. =Chætangiaceæ.= _Galaxaura_ has a thallus thickly
incrusted with lime.

Order 4. =Gelidiaceæ.= _Naccaria, Gelidium._

Sub-Family 2. =Gigartinales.= The fertilised auxiliary cell
grows towards the thallus, to produce the gonimoblasts.
Procarpia generally present.

Order 5. =Acrotylaceæ.= _Acrotylus._

Order 6. =Gigartinaceæ.= _Gigartina_, _Phyllophora_,
_Ahnfeltia_; _Chondrus crispus_, with dark red, dichotomously
branched thallus, is common on the coasts of Scandinavia and
Great Britain.

Order 7. =Rhodophyllidaceæ.= _Rhodophyllis_, _Euthora_;
_Cystoclonium purpurascens_ is common, and sometimes the ends of
its branches may be modified into tendril-like haptera.

Sub-Family 3. =Rhodymeniales.= The fertilised auxiliary cell
forms the gonimoblast on the side away from the thallus.
Procarpia are abundantly produced.

Order 8. =Sphærococcaceæ.= _Gracilaria._

Order 9. =Rhodymeniaceæ.= _Rhodymenia palmata_ is a common
species. _Lomentaria_, _Chylocladia_, _Plocamium_.

Order 10. =Delesseriaceæ.= _Delesseria sanguinea_; _D. alata_
and _D. sinuosa_ are handsome forms which are not uncommon.

Order 11. =Bonnemaisoniaceæ.= _Bonnemaisonia._

Order 12. =Rhodomelaceæ.= _Rhodomela_, _Odonthalia_;
_Polysiphonia_, of which many species are to be found on the
coasts of Great Britain, has a filamentous, richly branched
thallus consisting of a central row of cells surrounded by a
varying number of cortical cells of similar size--the so-called
“siphons.”

Order 13. =Ceramiaceæ.= Pretty Algæ, often branched
dichotomously, or unilaterally pinnate. _Spermothamnion,
Griffithsia, Callithamnion, Ceramium, Ptilota._

Sub-Family 4. =Cryptonemiales.= The cells formed by the
coalescence of the auxiliary cells and the ooblastema-filaments,
produce the gonimoblasts. The _carpogonium-filaments_ and
the auxiliary cells are scattered singly in the thallus.

Order 14. =Gloiosiphoniaceæ.= _Gloiopeltis._

Order 15. =Grateloupiaceæ.= _Halymenia, Cryptonemia._

Order 16. =Dumontiaceæ.= _Dumontia, Dudresnaya._

Order 17. =Nemastomaceæ.= _Furcellaria_, which has
dichotomously branched, round shoots, is common on the coasts of
Great Britain.

Order 18. =Rhizophyllidaceæ.= _Polyides, Rhizophyllis._

Order 19. =Squamariaceæ.= The Algæ belonging to this order
form crust-like coverings on stones, mussel-shells, and on
other Algæ, but are not themselves incrustated: _Petrocelis_,
_Cruoria_, _Peyssonellia_.

Order 20. =Corallinaceæ.= Partly crustaceous, partly erect,
branched Algæ, thickly incrusted with lime, so that a few
species (_Lithothamnia_, also called _Nullipora_) occur in
fossilized condition from Jurassic to Tertiary periods.
_Melobesia, Lithophyllum, Lithothamnion, Corallina._

USES. “Carragen” is the thallus of _Chondrus crispus_ (Irish Moss) and _Gigartina mamillosa_. It is a common article of food on the coasts of Ireland, and swells to a jelly when cooked. It is officinal. _Rhodymenia palmata_ is generally eaten as food in Ireland and in some places on the west coast of Norway; it is also used as food for sheep and hence is termed “Sheep-seaweed.” Agar-Agar is the jelly obtained from species of _Gelidium_ and _Gigartina_ growing in China and Japan.

Sub-Division III. =FUNGI.=

=Mode of Life.= The Fungi have no chlorophyll, and are thus unable in any stage of their existence to assimilate carbon; they must therefore live as _saprophytes_ or _parasites_. There is, however, no strong line of demarcation between these; many Fungi commence as true parasites, but only attain their full development upon or in dead plants or animals (_Rhytisma_, _Empusa_). Many saprophytes may occasionally appear as parasites, and are then designated “_facultative parasites_” (_Nectria cinnabarina_, _Lophodermium pinastri_), in contradistinction to those which only appear as parasites, “_obligate parasites_” (Mildew, Brand-and Rust-Fungi, _Cordyceps_).

The parasites which live on the surface of the host-plant are termed _epiphytic_ (Mildew, _Fusicladium_); and those living in its tissues are termed _endophytic_ (_Ustilago_, _Peronospora_). _Epizoic_ (_Oidium tonsurans_, _Laboulbenia_) and _endozoic_ Fungi (_Cordyceps_, _Entomophthora_), are distinguished, in the same manner, as those which live on the surface or in the interior of animals. The Fungi designated _pathogenic_ are especially those which produce disease in human beings and in animals.

Most of the diseases of plants are attributed to the parasitic Fungi. These force their way into the host-plant by piercing the outer wall of the epidermis, as in the Potato-disease; or by growing in through the stomata, _e.g._ the summer generations of the Rust of Wheat; or they can only penetrate through a wound, _e.g. Nectria_. Some effect an entrance into the host-plant by the secretion of a poisonous matter or ferment, which softens and destroys the cell-walls (_Sclerotinia_). Some Yeast and Mould Fungi secrete ferments (enzymes), which, for example, convert cane-sugar into a sugar capable of fermentation.

The relation of the parasitic Fungus to the host-plant is mainly of two kinds. In the one case, the cell-contents are destroyed, the protoplasm is killed, and the cellular tissue becomes discoloured and dies (_Peronospora_, _Armillaria mellea_, _Polyporus_); in the other case, the parasite has an irritating effect on the cellular tissue, whereby the affected organ grows more rapidly and becomes larger than normal, producing _hypertrophy_. Such malformations are termed _Fungi-galls_ (Mycocecidia); in this manner “witches’ brooms” are produced by _Æcidium_, “pocket-plum” by _Taphrina_, and other deformities by _Exobasidium_ and _Cystopus candidus_. This hypertrophy may either be produced by a vigorous cell-multiplication, which is most frequently the case, or by the enlargement of the individual cells (_Synchytrium_, _Calyptospora_). The relation between host and Fungus among the Lichens is of a very peculiar nature, termed “_symbiosis_.”

=Vegetative Organs.= The vegetative parts of a Fungus are termed its _mycelium_.[10] This is formed of a mass of long, cylindrical, branched cells resembling threads (and hence termed _hyphæ_), which have a continued apical growth. The mycelium, in its early development, shows a well-marked difference between the two main groups of true Fungi: in the _Phycomycetes_, or Algal Fungi, the mycelium has no transverse walls, and is therefore unicellular, while in the _Mesomycetes_ and _Mycomycetes_ it is provided with dividing walls, which gradually arise during growth, in the youngest hyphæ; intercalary transverse walls may also be formed at a later period. In the hyphæ of some of the Higher Fungi (_Hymenomycetes_), connections may be formed between two contiguous cells of the same hypha, by a protuberance growing out from an upper cell just above the transverse wall, and forming a junction with the cell below. These are known as _clamp-connections_; they appear to be of use in affording communication between the two cells.

The hyphæ of Fungi, where they come in contact with one another, often grow together, so that =H=-formed combinations (fusions) are produced, which give rise to very compact felted tissue. When the hyphæ are not only closely interwoven, but also united and provided with many transverse walls, the mycelium assumes the appearance of a tissue with isodiametric cells, and is then termed _pseudo-parenchyma_. The hyphæ-walls are sometimes very much thickened, and composed of several layers, and the external layers, by the absorption of water, may often swell very much and become mucilaginous. In some instances the walls are colourless, in others coloured, the most frequent colour being brown. The cell-contents may also be coloured, and in that case are generally yellow; this colour is chiefly connected with the fat (oil) which may be found in abundance in the Fungi, whilst starch is invariably absent in all the true Fungi.

The mycelium assumes many different forms; sometimes it appears as a thread-like, cobwebby, loose tissue, less frequently as firm strands, thin or thick membranes, horn-like plates or tuber-like bodies. The _thread-like_ mycelium may, in the parasitic Fungi, be intercellular or intracellular, according as it only extends into the interstices between the cells or enters into the cells proper. In the first case there are generally found haustoria, or organs of suction (_e.g._ among the _Peronosporaceæ_; _Taphrina_, on the contrary, has no haustoria); but haustoria are also found among the epiphytic Fungi (_e.g._ Erysiphaceæ). Intracellular mycelia are found in the Rust-Fungi, in _Claviceps purpurea_, _Entomophthora_, etc. In spite of its delicate structure, this mycelium may live a long time, owing to the circumstance that it continues to grow peripherally, while the older parts gradually die off (“fairy rings”).

_String-like_ mycelia may be found, for example, in _Phallus_, _Coprinus_, and are formed of hyphæ, which run more or less parallel to each other. _Membrane-like_ mycelia are chiefly to be found in Fungi growing on tree-stems (Polyporaceæ and Agaricaceæ); they may have a thickness varying from that of the finest tissue-paper to that of thick leather, and may extend for several feet. The peculiar horny or leather-like strands and plates which, for instance, appear in _Armillaria mellea_, are known as _Rhizomorpha_; they may attain a length of more than fifty feet. The _tuber-like_ mycelia or _sclerotia_ play the part of resting mycelia, since a store of nourishment is accumulated in them, and after a period of rest they develope organs of reproduction. The sclerotia are hard, spherical, or irregular bodies, from the size of a cabbage seed to that of a hand, internally white or greyish, with a brown or black, pseudo-parenchymatous, external layer. Sclerotia only occur in the higher Fungi, and are found both in saprophytes, _e.g. Coprinus_, and in parasites, _e.g. Claviceps_ (Ergot), _Sclerotinia_.

=Reproduction.= SEXUAL REPRODUCTION is found only among the lower Fungi which stand near to the Algæ, the Algal-Fungi, and takes place by the same two methods as in the Algæ, namely by _conjugation_ and by the _fertilisation_ of the egg-cell in the oogonium.

The majority of Fungi have only ASEXUAL reproduction. The most important methods of this kind of reproduction are the _sporangio-fructification_ and the _conidio-fructification_.

In the SPORANGIO-FRUCTIFICATION the _spores_ (endospores) _arise inside_ a mother-cell, the sporangium (Fig. 80). Spores without a cell-wall, which move in water by means of cilia and hence are known as _swarmspores_ or _zoospores_, are found among the Oomycetes, the sporangia in which these are produced being called swarm-sporangia or zoosporangia (Figs. 86, 87, 91, 94).

In the CONIDIO-FRUCTIFICATION the _conidia_ (exospores) arise on special hyphæ (conidiophores), or directly from the mycelium. When conidiophores are present, the conidia are developed upon them terminally or laterally, either in a basipetal succession (in many Fungi, for example in _Penicillium_, Fig. 111, _Erysiphe_, _Cystopus_), or acropetally (in which method the chains of conidia are often branched; examples, _Pleospora vulgaris_, _Hormodendron cladosporioides_). All conidia are at first unicellular, sometimes at a later stage they become two-celled or multicellular through the formation of partition-walls (_Piptocephalis_). The conidia with thick, brown cell-walls, and contents rich in fats (_resting conidia_), can withstand unfavourable external conditions for a much longer period than conidia with thin walls and poor in contents.

The SPORANGIA arise either from the ordinary cells of the mycelium (_Protomyces_), or are borne on special hyphæ. They are generally spherical (_Mucor_, Fig. 80; Saprolegniaceæ), egg-, pear-, or club-shaped (Ascomycetes), more rarely they are cylindrical or spindle-shaped. While among the Phycomycetes the size, form, and number of spores are indefinite in each species, in the Ascomycetes the sporangia (_asci_) have a definite size, form, and number of spores. The spores of the Ascomycetes are known as ascospores.

The sporangio-fructification is found under three main forms.

1. FREE SPORANGIOPHORES which are either single (_Mucor_, Fig. 78), or branched (_Thamnidium_).

2. SPORANGIAL-LAYERS. These are produced by a number of sessile or shortly-stalked sporangia, being formed close together like a palisade (_Taphrina_, Fig. 105).

3. SPORANGIOCARPS. These consist usually of many sporangia enclosed in a covering, they are found only in the Carpoasci, and are also known as _ascocarps_. The parts of an ascocarp are the _covering_ (_peridium_), and the _hymenium_, which is in contact with the inner wall of the peridium, and is generally made up of asci, and sterile, slender hyphæ. The latter either penetrate between the asci and are branched and multicellular (_paraphyses_, Figs. 103 _d_, 123, 125, 129), or clothe those parts of the inner wall which bear no asci (_periphyses_; among many peronocarpic Ascomycetes, _e.g. Chætomium_, _Sordaria_, _Stictosphæra hoffmanni_). The ascocarps are produced directly from the mycelium, or from a _stroma_, that is a vegetative body of various forms, in which they may be embedded (Figs. 116 _B_, _C_).

Among the conidio-fructifications there are, in the same way, three divisions.

1. FREE CONIDIOPHORES (Fig. 109). The form of the conidiophores, the shape, and number of its spores are various. In the most highly developed Fungi, the Basidiomycetes, there are, however, special more highly developed conidiophores, the _basidia_, which have a definite form and spores of a definite shape and number. The conidia borne on basidia are called _basidiospores_.

2. CONIDIAL-LAYERS. (_a_) The SIMPLEST case of this is found when the conidiophores arise directly from the mycelium, parallel to one another, and form a flat body (_e.g. Exobasidium vaccinii_, _Hypochnus_; among the Phycomycetes, _Empusa muscæ_ and _Cystopus_). (_b_) In a HIGHER form the conidial-layers are thick, felted threads (_stroma_) inserted between the mycelium and the _hymenium_ (_i.e._ the region of the conidiophores). Examples are found in a section of the Pyrenomycetes (Fig. 122). (_c_) The HIGHEST form has the _basidial-layer_, that is a conidial-layer with more highly developed conidiophores (basidia). The basidial-layer, with stroma, and the hymenium (region of the basidia), forms the basidio-fructification, which is branched in the Clavariaceæ, and hat-shaped in other Hymenomycetes (in these groups the hymenium is confined to the lower side of the pileus).

The hymenium of the conidial-layer and basidial-layer is composed entirely of conidiophores, or of conidiophores and sterile hyphæ (_paraphyses_) which are probably always unicellular. Paraphyses are found in _Entomophthora radicans_, and in certain Basidiomycetes (_e.g. Corticium_).

3. CONIDIOCARPS (_pycnidia_). A special covering surrounds the conidia-forming elements. The inner side of this covering (_peridium_) bears the hymenium, _i.e._ those elements from which the conidia are abstricted. The conidiocarps arise either immediately from the hyphæ or from a _stroma_ in which they are generally embedded. Conidiocarps are entirely wanting in the Phycomycetes. On the other hand they are found among the Ascomycetes and Basidiomycetes, and in the latter group the conidiocarps contain more highly differentiated conidiophores (basidia) and are known as _basidiocarps_. Conidiocarps with simple conidiophores, are found only among the Basidiomycetes, in the Uredinaceæ, and in _Craterocolla cerasi_. In the Ascomycetes (Figs. 120 _d_, _e_; 117 _a_, _b_; 123 _a_; 124 _b_) the conidiocarps are visible, as points, to the naked eye, while the basidiocarps of the Basidiomycetes (Figs. 170, 171, 173–176, 178–180) vary from the size of a pea to that of a child’s head. The “spermogonia” of the Ascomycetes and Lichenes, are conidiocarps with small conidia (_microconidia_) which germinate sometimes more slowly than other conidia, and formerly were erroneously considered as male reproductive cells, and called spermatia.

The conidia of the Fungi are not primitive structures. The comparison of the sporangia and conidia among the Zygomycetes, and among the species of the genus _Peronospora_ shows, that the conidia are aberrant formations, and that they have arisen through the degeneration of the sporangium, which, by the reduction of its spores to one, has itself become a spore.

In the genera _Thamnidium_ and _Chætocladium_ the gradual
diminution of the sporangia, and the reduction of the number
of spores can be distinctly followed. In _Thamnidium_ the
number of spores is often reduced to one, which is _free_ in
the sporangium. In _Chætocladium_ however the sporangia are
typically _one-spored_, the spore is always united with the
sporangium, and the two become a single body, the so-called
_conidium_, which is in reality a closed sporangium. How
close is the connection between the sporangia and conidia of
_Thamnidium_ and _Chætocladium_, is seen from the fact that,
in the conidial stage of _Chætocladium_ the same whorl-form of
branching appears as in the sporangial stages of _Thamnidium
chætocladioides_, and also, that the conidia of _Ch.
fresenianum_ throw off the former sporangium-wall (exosporium),
while _Ch. jonesii_ germinates without shedding its exosporium.
The Phycomycetes have doubtless sprung from Water-Algæ and
inherit the sporangia from them. On this supposition, as the
Phycomycetes assumed a terrestrial mode of life, the sporangia
would become adapted to the distribution of the spores by
means of the air, the sporangia would become small, contain
dust-like spores, and would eventually become closed-sporangia,
_i.e._ conidia. The conidia are a terrestrial method for the
multiplication of Fungi. In the Hemiasci and the Ascomycetes the
sporangia are still preserved, but in every instance they are
adapted to terrestrial spore-distribution, their spores being
set free on the destruction of the sporangium-wall (generally
shot out) and distributed through the air. For further examples
of spore-distribution see below, p. 91–93.

The reproduction of Fungi is accomplished not only by spores and conidia, but also sometimes by _chlamydospores_. These are fundaments[11] of sporangiophores and conidiophores, which have taken on a resting condition in the form of a spore, and are able to germinate and produce carpophores. In the formation of the chlamydospores the hyphæ accumulate reserve materials at the expense of the neighbouring cells; in the undivided hyphæ of the Phycomycetes transverse walls are formed, and finally the chlamydospores are set free by the decay of the empty cells connecting them with the mycelium. One must distinguish between _oidia_ and _true chlamydospores_. The former are more simple, the latter are a somewhat more differentiated form of carpophore fundaments, which serve for propagation in the same manner as spores. In _Chlamydomucor racemosus_ the chlamydospores grow out into the air and form differentiated carpophores. In the Autobasidiomycetes they only germinate vegetatively, and not with the formation of fructifications. From _Chlamydomucor_ up to the Autobasidiomycetes the successive development of the fructification, which is interrupted by the formation of the chlamydospores, degenerates more and more. Among certain Ustilagineæ the chlamydospores (brand-spores) no longer germinate with the production of fructifications. In the Uredinaceæ, only one of the three chlamydospore-forms has the property of producing fructifications on germination; the other forms only germinate vegetatively, like ordinary spores, and in the same manner as the chlamydospores of the Autobasidiomycetes. In the Hemibasidii, and the Uredinaceæ, in _Protomyces_, the chlamydospores are the chief means of reproduction. They are found also among the Ascomycetes.

The sporangia and the conidia of the Fungi have their common origin in the sporangia of the Phycomycetes. The asci (and the Ascomycetes which are characterised by these bodies) are descended from the sporangia-forming, lower Fungi; the basidia (and the Basidiomycetes) from those which bear conidia. _The sporangia of the Phycomycetes are the primitive form and the starting point for all the reproductive forms of the Fungi._ The chlamydospores appear besides in all classes of Fungi as supplementary forms of reproduction, and are of no importance in determining relationships. Although the expression “fruit” must essentially be applied to true Phanerogams, yet, through usage, the term “_fruit-forms_,” is employed to designate the forms or means of reproduction of Fungi, and the organs of reproduction are known as _organs of fructification_, the sporangiophores and conidiophores as _fruit-bearers_ (_carpophores_), and the sporangiocarps, conidiocarps, and basidiocarps as “_fruit-bodies_.”

The majority of Fungi have more than one method of reproduction,
often on various hosts (Uredinaceæ). Species with one, two,
or more than two methods of reproduction are spoken of as
having monomorphic, dimorphic, or pleomorphic fructification.
Monomorphic, _e.g._ the Tuberaceæ; dimorphic, _Mucor_,
_Piptocephalis_, Saprolegniaceæ, _Penicillium crustaceum_;
pleomorphic, _Puccinia graminis_, _Capnodium salicinum_ (in the
last species there are five methods of reproduction: yeast-like
conidia, free conidiophores, conidiocarps with small and large
conidia, and ascocarps).

=The liberation and distribution of the spores and conidia.= The spores and conidia, on account of their small size and lightness, are spread far and wide by currents in the air, but in addition to this method, insects and other animals frequently assist in disseminating them. The liberation of the conidia is occasionally effected by the complete shrinking away of the conidiophore, but more frequently by abstriction from the conidiophores, either by their gradually tapering to a point, or by the dissolution of a cross-wall (generally of a mucilaginous nature). The individual links of conidia-chains are detached from one another in the same way, or often by means of small, intercalary cells, which are formed at the base of the individual links, and becoming slimy, dissolve upon the maturity of the spores. Special contrivances for ejecting the spores and conidia may often be found. In _Peronospora_ the cylindrical fruit-hyphæ in the dry condition become strap-shaped and also twisted. These are very hygroscopic, and the changes of form take place so suddenly, that the spores are violently detached and shot away. In _Empusa_ a peculiar squirting mechanism may be found (Fig. 85). Each club-shaped hypha which projects from the body of the fly, bears a conidium at its apex; a vacuole, which grows gradually larger, is formed in the slimy contents of the hypha, and the pressure thereby eventually becomes so great that the hypha bursts at its apex, and the conidium is shot into the air. By a similar mechanism, the spores of many of the Agaricaceæ are cast away from the parent-plants. In the case of _Pilobolus_ (Fig. 84) the entire sporangium is thrown for some distance into the air by a similar contrivance, the basal region of the sporangium having, by the absorption of water, been transformed into a slimy layer which is readily detached. _Sphærobolus_, a Gasteromycete, has a small, spherical fruit-body (basidiocarp), the covering of which, when ripe, suddenly bursts, and the basidiospores contained in it are forcibly ejected.