Chapter III: DISTRIBUTION.--Grasses are the most universally diffused of all

flowering plants. There is no district in which they do not occur, and in nearly all they are a leading feature of the flora. In number of species Gramineae comes considerably after Compositae and Leguminosae, the two most numerous orders of phanerogams, but in number of individual plants it probably far exceeds either; whilst from the wide extension of many of its species, the proportion of Gramineae to other orders in the various floras of the world is much higher than its number of species would lead one to expect. In tropical regions, where Leguminosae is the leading order, grasses closely follow as the second, whilst in the warm and temperate regions of the northern hemisphere, in which Compositae takes the lead, Gramineae again occupies the second position.

While the greatest number of species is found in the tropical zone, the number of individuals is greater in the temperate zones, where they form extended areas of turf. Turf- or meadow-formation depends upon uniform rainfall. Grasses also characterize steppes and savannas, where they form scattered tufts. The bamboos are a feature of tropical forest vegetation, especially in the monsoon region. As the colder latitudes are entered the grasses become relatively more numerous, and are the leading family in Arctic and Antarctic regions. The only countries where the order plays a distinctly subordinate part are some extra-tropical regions of the southern hemisphere, Australia, the Cape, Chili, &c. The proportion of graminaceous species to the whole phanerogamic flora in different countries is found to vary from nearly 1/4th in the Arctic regions to about 1/25th at the Cape; in the British Isles it is about 1/12th.

The principal climatic cause influencing the number of graminaceous species appears to be amount of moisture. A remarkable feature of the distribution of grasses is its uniformity; there are no great centres for the order, as in Compositae, where a marked preponderance of endemic species exists; and the genera, except some of the smallest or monotypic ones, have usually a wide distribution.

The distribution of the tropical tribe _Bambuseae_ is interesting. The species are about equally divided between the Indo-Malayan region and tropical America, only one species being common to both. The tribe is very poorly represented in tropical Africa; one species _Oxytenanthera abyssinica_ has a wide range, and three monotypic genera are endemic in western tropical Africa. None is recorded for Australia, though species may perhaps occur on the northern coast. One species of _Arundinaria_ reaches northwards as far as Virginia, and the elevation attained in the Andes by some species of _Chusquea_ is very remarkable,--one, _C. aristata_, being abundant from 15,000 ft. up to nearly the level of perpetual snow.

Many grasses are almost cosmopolitan, such as the common reed, _Phragmites communis_; and many range throughout the warm regions of the globe, e.g. _Cynodon Dactylon_, _Eleusine indica_, _Imperata arundinacea_, _Sporobolus indicus_, &c., and such weeds of cultivation as species of _Setaria_, _Echinochloa_. Several species of the north temperate zone, such as _Poa nemoralis_, _P. pratensis_, _Festuca ovina_, _F. rubra_ and others, are absent in the tropics but reappear in the antarctic regions; others (e.g. _Phleum alpinum_) appear in isolated positions on high mountains in the intervening tropics. No tribe is confined to one hemisphere and no large genus to any one floral region; facts which indicate that the separation of the tribes goes back to very ancient times. The revision of the Australian species by Bentham well exhibits the wide range of the genera of the order in a flora generally so peculiar and restricted as that of Australia. Thus of the 90 indigenous genera (many monotypic or very small) only 14 are endemic, 1 extends to South Africa, 3 are common to Australia and New Zealand, 18 extend also into Asia, whilst no fewer than 54 are found in both the Old and New Worlds; 26 being chiefly tropical and 28 chiefly extra-tropical.

Of specially remarkable species _Lygeum_ is found on the sea-sand of the eastern half of the Mediterranean basin, and the minute _Coleanthus_ occurs in three or four isolated spots in Europe (Norway, Bohemia, Austria, Normandy), in North-east Asia (Amur) and on the Pacific coast of North America (Oregon, Washington). Many remarkable endemic genera occur in tropical America, including _Anomochloa_ of Brazil, and most of the large aquatic species with separated sexes are found in this region. The only genus of flowering plants peculiar to the arctic regions is the beautiful and rare grass _Pleuropogon Sabinii_, of Melville Island.

_Fossil Grasses._--While numerous remains of grass-like leaves are a proof that grasses were widespread and abundantly developed in past geological ages, especially in the Tertiary period, the fossil remains are in most cases too fragmentary and badly preserved for the determination of genera, and conclusions based thereon in explanation of existing geographical distribution are most unsatisfactory. There is, however, justification for referring some specimens to _Arundo_, _Phragmites_, and to the _Bambuseae_.

BIBLIOGRAPHY.--E. Hackel, _The True Grasses_ (translated from Engler
and Prantl, _Die naturlichen Pflanzenfamilien_, by F. Lamson Scribner
and E. A. Southworth); and _Andropogoneae_ in de Candolle's
_Monographiae phanerogamarum_ (Paris, 1889); K. S. Kunth, _Revision
des graminees_ (Paris, 1829-1835) and _Agrostographia_ (Stuttgart,
1833); J. C. Doll in Martius and Eichler, _Flora Brasiliensis_, ii.
Pts. II. and III. (Munich, 1871-1883); A. W. Eichler,
_Bluthendiagramme_ i. 119 (Leipzig, 1875); Bentham and Hooker, _Genera
plantarum_, iii. 1074 (London, 1883); H. Baillon, _Histoire des
plantes_, xii. 136 (Paris, 1893); J. S. Gamble, "_Bambuseae_ of
British India" in _Annals Royal Botanic Gardens, Calcutta_, vii.
(1896); John Percival, _Agricultural Botany_ (chapters on "Grasses,"
2nd ed., London, 1902). See also accounts of the family in the various
great floras, such as Ascherson and Graebner, _Synopsis der
mitteleuropaischen Flora_; N. L. Britton and A. Brown, _Illustrated
Flora of the Northern United States and Canada_ (New York, 1896);
Hooker's _Flora of British India_; _Flora Capensis_ (edited by W.
Thiselton-Dyer); Boissier, _Flora orientalis_, &c. &c.

FOOTNOTE:

[1] The word "grass" (O. Eng. _gaers_, _graes_) is common to Teutonic
languages, cf. Dutch Ger. Goth, _gras_, Dan. _graes_; the root is the
O. Teut. _gra_-, _gro_-, to increase, whence "grow," and "green," the
typical colour of growing vegetation. The Indo-European root is seen
in Lat. _gramen_. The O. Eng. _grasian_, formed from _graes_, gives
"to graze," of cattle feeding on growing herbage, also "grazier," one
who grazes or feeds cattle for the market; "to graze," to abrade, to
touch lightly in passing, may be a development of this from the idea
of close cropping; if it is to be distinguished a possible connexion
may be found with "glace" (Fr. _glacer_, glide, slip, Lat. _glacies_,
ice), to glance off, the change in form being influenced by "grate,"
to scrape, scratch (Fr. _gratter_, Ger. _kratzen_).