Chapter IV: Part 4

In a similar manner, protein seems to be changed and transferred to various parts of the plant. Some forms of protein substance are _soluble_ and others _insoluble_ in water. White of egg, for example, is slightly soluble, but can be rendered insoluble by heating it so that it coagulates. Insoluble proteins are digested within the plant; how and where is but slightly understood. In a plant, soluble proteins pass down the sieve tubes in the bast and then may be stored in the bast or medullary rays of the wood in an insoluble form, or they may pass into the fruit or seeds of a plant, and be stored there.

What forces Water up the Stem.--We have seen that the process of osmosis is responsible for taking in soil water, and that the enormous absorbing surface exposed by the root hairs makes possible the absorption of a large amount of water. Frequently this is more than the weight of the plant in every twenty-four hours.

Experiments have been made which show that at certain times in the year this water is in some way forced up the tiny tubes of the stem. During the spring season, in young and rapidly growing trees, water has been proved to rise to a height of nearly ninety feet. The force that causes this rise of water in stems is known as _root pressure_.

The greatest factor, however, is transpiration of water from leaves. This evaporation of water in the form of vapor seems to result in a kind of suction on the column of water in the stem. In the fall, after the leaves have gone, much less water is taken in by roots, showing that an intimate relation exists between the leaves and the root.

Summary of the Functions of Green Plants.--The processes which we have just described (with the exception of food making) are those which occur in the lives of any plant or animal. All plants and animals breathe, they oxidize their foods to release energy, carbon dioxide being given off as the result of the union of the carbon in the foods with the oxygen of the air. Both plants and animals digest their food; plants may do this in the cells of the root, stem, and leaf. Digestion must always occur so that food can be moved in a soluble condition from cell to cell in the plant's body.

Plants with Special Digestive Organs.--Some plants have special organs of digestion. One of these, the sundew, has leaves which are covered on one side with tiny glandular hairs. These attract insects and later serve to catch and digest the nitrogenous matter of these insects by means of enzymes poured out by the same hairs. Another plant, the Venus fly trap, catches insects in a sensitive leaf which folds up and holds the insect fast until enzymes poured out by the leaf slowly digest it. Still others, called pitcher plants, use as food the decayed bodies of insects which fall into their cuplike leaves and die there. In this respect plants are like those animals which have certain organs in the body set apart for the digestion of food.

Assimilation.--The assimilation of foods, or making of foods into living matter, is a process we know very little about. We know it takes place in the living cells of plants and animals. But how foods are changed into living matter is one of the mysteries of life which we have not yet solved.

Excretion.--The waste and repair of living matter seems to take place in both plants and animals. When living plants breathe, they give off carbon dioxide. In the process of starch-making, oxygen might be considered the waste product. Water is evaporated from leaves and stems. The leaves fall and carry away waste mineral substances which they contain.

Reproduction.--Finally, both plants and animals have organs of reproduction. We have seen that the flower gives rise, after pollination, to a fruit which holds the seeds. These seeds hold the _embryo_. Thus the young plant is doubly protected for a time and is finally thrown off in the seed with enough food to give it a start in life. In much the same way we will find that animals reproduce, either by laying eggs which contain an _embryo_ and food to start it in life or, as in the higher animals, by holding and protecting the embryo within the body of the mother until it is born, a helpless little creature, to be tenderly nourished by the mother until able to care for itself.

The Life Cycle.--Ultimately both plants and animals grow old and die. Some plants, for example the pea or bean, live but a season; others, such as the big trees of California, live for hundreds of years. Some insects exist as adults but a day, while the elephant is said to live almost two hundred years. The span of life from the time the plant or animal begins to grow until it dies is known as the _life cycle_.

REFERENCE BOOKS

ELEMENTARY

Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Andrews, _A Practical Course in Botany_, pages 112-127.
American Book Company.
Atkinson, _First Studies of Plant Life_, Chaps. IV, V, VI,
VIII, XXI. Ginn.
Coulter, _Plant Life and Plant Uses_, Chap. V. American Book
Company.
Dana, _Plants and their Children_, pages 99-129. American
Book Company.
Mayne and Hatch, _High School Agriculture_. American Book
Company.
Hodge, _Nature Study and Life_, Chaps. IX, X, XI. Ginn and
Company.
MacDougal, _The Nature and Work of Plants_. The Macmillan
Company.

ADVANCED

Apgar, _Trees of the United States_, Chaps. II, V, VI.
American Book Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Vol. I.
American Book Company.
Duggar, _Plant Physiology_. The Macmillan Company.
Ganong, _The Teaching Botanist_. The Macmillan Company.
Goebel, _Organography of Plants_, Part V. Clarendon Press.
Goodale, _Physiological Botany_. American Book Company.
Gray, _Structural Botany_, Chap. V. American Book Company.
Kerner-Oliver, _Natural History of Plants_. Henry Holt and
Company.
Strasburger, Noll, Schenck, and Karston, _A Textbook of
Botany_. The Macmillan Company.
Ward, _The Oak_. D. Appleton and Company.
Yearbook, U. S. Department of Agriculture, 1894, 1895,
1898-1910.

IX. OUR FORESTS, THEIR USES AND THE NECESSITY FOR THEIR PROTECTION

_Problem.--Man's relations to forests._
_(a) What is the value of forests to man?_
_(b) What can man do to prevent forest destruction?_

LABORATORY SUGGESTIONS

Demonstration of some uses of wood. Optional exercise on
structure of wood. Method of cutting determined by
examination. Home work on study of furniture trim, etc.
Visit to Museum to study some economic uses of wood.
Visit to Museum or field trip to learn some common trees.

The Economic Value of Trees. Protection and Regulation of Water Supply.--Trees form a protective covering for parts of the earth's surface. They prevent soil from being washed away, and they hold moisture in the ground. The devastation of immense areas in China and considerable damage by floods in parts of Switzerland, France, and in Pennsylvania has resulted where the forest covering has been removed. No one who has tramped through our Adirondack forest can escape noticing the differences in the condition of streams surrounded by forest and those which flow through areas from which trees have been cut. The latter streams often dry up entirely in hot weather, while the forest-shaded stream has a never failing supply of crystal water.

The city of New York owes much of its importance to its position at the mouth of a great river with a harbor large enough to float the navies of the world. This river is supplied with water largely from the Adirondack and Catskill forests. Should these forests be destroyed, it is not impossible that the frequent freshets which would follow would so fill the Hudson River with silt and debris that the ship channels in the bay, already costing the government hundreds of thousands of dollars a year to keep dredged, would become too shallow for ships. If this _should_ occur, the greatest city in this country would soon lose its place and become of second-rate importance.

The story of how this very thing happened to the old Greek city of Poseidonia is graphically told in the following lines:--

"It was such a strange, tremendous story, that of the Greek
Poseidonia, later the Roman Paestum. Long ago those
adventuring mariners from Greece had seized the fertile
plain, which at that time was covered with forests of great
oak and watered by two clear and shining rivers. They drove
the Italian natives back into the distant hills, for the
white man's burden even then included the taking of all the
desirable things that were being wasted by incompetent
natives, and they brought over colonists--whom the
philosophers and moralists at home maligned, no doubt, in
the same pleasant fashion of our own day. And the colonists
cut down the oaks, and plowed the land, and built cities,
and made harbors, and finally dusted their busy hands and
busy souls of the grime of labor and wrought splendid
temples in honor of the benign gods who had given them the
possessions of the Italians and filled them with power and
fatness.

"Every once in so often the natives looked lustfully down
from the hills upon this fatness, made an armed snatch at
it, were driven back with bloody contumely, and the heaping
of riches upon riches went on. And more and more the oaks
were cut down--mark that! for the stories of nations are so
inextricably bound up with the stories of trees--until all
the plain was cleared and tilled; and then the foothills
were denuded, and the wave of destruction crept up the
mountain sides, and they, too, were left naked to the sun
and the rains.

"At first these rains, sweeping down torrentially,
unhindered by the lost forests, only enriched the plain with
the long-hoarded sweetness of the trees; but by and by the
living rivers grew heavy and thick, vomiting mud into the
ever shallowing harbors, and the land soured with the
undrained stagnant water. Commerce turned more and more to
deeper ports, and mosquitoes began to breed in the brackish
soil that was making fast between the city and the sea.

"Who of all those powerful landowners and rich merchants
could ever have dreamed that little buzzing insects could
sting a great city to death? But they did. Fevers grew more
and more prevalent. The malaria haunted population went more
and more languidly about their business. The natives, hardy
and vigorous in the hills, were but feebly repulsed.
Carthage demanded tribute, and Rome took it, and changed the
city's name from Poseidonia to Paestum. After Rome grew weak,
Saracen corsairs came in by sea and grasped the slackly
defended riches, and the little winged poisoners of the
night struck again and again, until grass grew in the
streets, and the wharves crumbled where they stood. Finally,
the wretched remnant of a great people wandered away into
the more wholesome hills, the marshes rotted in the heat and
grew up in coarse reeds where corn and vine had flourished,
and the city melted back into the wasted earth."[16]

Footnote 16: Elizabeth Bisland and Anne Hoyt, _Seekers in
Sicily_. John Lane Company.

Prevention of Erosion by Covering of Organic Soil.--We have shown how ungoverned streams might dig out soil and carry it far from its original source. Examples of what streams have done may be seen in the deltas formed at the mouths of great rivers. The forest prevents this by holding the water supply and letting it out gradually. This it does by covering the inorganic soil with humus or decayed organic material. In this way the forest floor becomes like a sponge, holding water through long periods of drought. The roots of the trees, too, help hold the soil in place. The gradual evaporation of water through the stomata of the leaves cools the atmosphere, and this tends to precipitate the moisture in the air. Eventually the dead bodies of the trees themselves are added to the organic covering, and new trees take their place.

Other Uses of the Forest.--In some localities forests are used as windbreaks and to protect mountain towns against avalanches. In winter they moderate the cold, and in summer reduce the heat and lessen the danger from storms. Birds nesting in the woods protect many valuable plants which otherwise might be destroyed by insects.

Forests have great commercial importance. Pyrogallic and other acids are obtained from trees, as are tar, creosote, resin, turpentine, and many useful oils. The making of maple sirup and sugar forms a profitable industry in several states.

The Forest Regions of the United States.--The combined area of all the forests in the United States, exclusive of Alaska, is about 500,000,000 acres. This seemingly immense area is rapidly decreasing in acreage and in quality, thanks to the demands of an increasing population, a woeful ignorance on the part of the owners of the land, and wastefulness on the part of cutters and users alike.

A glance at the map on page 109 shows the distribution of our principal forests. Washington ranks first in the production of lumber. Here the great Douglas fir, one of the "evergreens," forms the chief source of supply. In the Southern states, especially Louisiana and Mississippi, yellow pine and cypress are the trees most lumbered.

Which states produce the most hardwoods? From which states do we get most of our yellow pine, spruce, red fir, redwood? Where are the heaviest forests of the United States?

Uses of Wood.--Even in this day of coal, wood is still by far the most used fuel. It is useful in building. It outlasts iron under water, in addition to being durable and light. It is cheap and, with care of the forests, inexhaustible, while our mineral wealth may some day be used up. Distilled wood gives wood alcohol. Partially burned wood is charcoal. In our forests much of the soft wood (the cone-bearing trees, spruce, balsam, hemlock, and pine), and poplars, aspens, basswood, with some other species, make paper pulp. The daily newspaper and cheap books are responsible for inroads on our forests which cannot well be repaired. It is not necessary to take the largest trees to make pulp wood. Hence many young trees of not more than six inches in diameter are sacrificed. Of the hundreds of species of trees in our forests, the conifers are probably most sought after for lumber. Pine, especially, is probably used more extensively than any other wood. It is used in all heavy construction work, frames of houses, bridges, masts, spars and timber of ships, floors, railway ties, and many other purposes. Cedar is used for shingles, cabinetwork, lead pencils, etc.; hemlock and spruce for heavy timbers and, as we have seen, for paper pulp. Another use for our lumber, especially odds and ends of all kinds, is in the packing-box industry. It is estimated that nearly 50 per cent of all lumber cut ultimately finds its way into the construction of boxes. Hemlock bark is used for tanning.

The hard woods--ash, basswood, beech, birch, cherry, chestnut, elm, maple, oak, and walnut--are used largely for the "trim" of our houses, for manufacture of furniture, wagon or car work, and endless other purposes.

Methods of cutting Timber.--A glance at the diagram of the sections of timber shows us that a tree may be cut radially through the middle of the trunk or tangentially to the middle portion. Most lumber is cut tangentially. In wood cut in this manner the yearly rings take a more or less irregular course. The grain in wood is caused by the fibers not taking straight lines in their course in the tree trunk. In many cases the fibers of the wood take a spiral course up the trunk, or they may wave outward to form little projections. Boards cut out of such a piece of wood will show the effect seen in many of the school desks, where the annual rings appear to form elliptical markings. Quite a difference in color and structure is often seen between the heartwood, composed of the dead walls of cells occupying the central part of the tree trunk, and the sapwood, the living part of the stem.

Knots.--Knots, as can be seen from the diagram, are branches which at one time started in their outward growth and were for some reason killed. Later, the tree, continuing in its outward growth, surrounded them and covered them up. A dead limb should be pruned before such growth occurs. The markings in bird's-eye maple are caused by buds which have not developed, and have been overgrown with the wood of the tree.

Destruction of the Forest.--_By Waste in Cutting._--Man is responsible for the destruction of one of this nation's most valuable assets. This is primarily due to wrong and wasteful lumbering. Hundreds of thousands of dollars' worth of lumber is left to rot annually because the lumbermen do not cut the trees close enough to the ground, or because through careless felling of trees many other smaller trees are injured. There is great waste in the mills. In fact, man wastes in every step from the forest to the finished product.

_By Fire._--Indirectly, man is responsible for fire, one of the greatest enemies of the forest. Most of the great forest fires of recent years, the losses from which total in the hundreds of millions, have been due either to railroads or to carelessness in making fires in the woods. It is estimated that in forest lands traversed by railroads from 25 per cent to 90 per cent of the fires are caused by coal-burning locomotives. For this reason laws have been made in New York State requiring locomotives passing through the Adirondack forest preserve to burn oil instead of coal. This has resulted in a considerable reduction in the number of fires. In addition to the loss in timber, the fires often burn out the organic matter in the soil (the "duff") forming the forest floor, thus preventing the growth of forest there for many years to come. In New York and other states fires are fought by an organized corps of fire wardens, whose duty it is to watch the forest and to fight forest fires.

Other Enemies.--Other enemies of the forest are numerous fungus plants, insect parasites which bore into the wood or destroy the leaves, and grazing animals, particularly sheep. Wind and snow also annually kill many trees.

Forestry.--In some parts of central Europe, the value of the forests was seen as early as the year 1300 A.D., and many towns consequently bought up the surrounding forests. The city of Zurich has owned forests in its vicinity for at least 600 years and has found them a profitable investment. In this country only recently has the importance of preserving and caring for our forests been noted by our government. Now, however, we have a Forest Survey of the Department of Agriculture and numerous state and university schools of forestry which are rapidly teaching the people of this country the best methods for the preservation of our forests. The Federal government has set aside a number of tracts of mountain forest in some of the Western states, making a total area of over 167,000,000 acres. New York has established for the same purpose the Adirondack Park, with nearly 1,500,000 acres of timberland. Pennsylvania has one of 700,000 acres, and many other states have followed their example.

Methods for Keeping and Protecting the Forests.--Forests should be kept thinned. Too many trees are as bad as too few. They struggle with one another for foothold and light, which only a few can enjoy. In cutting the forest, it should be considered as a harvest. The oldest trees are the "ripe grain," the younger trees being left to grow to maturity. Several methods of renewing the forest are in use in this country. (1) Trees may be cut down and young ones allowed to sprout from cut stumps. This is called coppice growth. This growth is well seen in parts of New Jersey. (2) Areas or strips may be cut out so that seeds from neighboring trees are carried there to start new growth. (3) Forests may be artificially planted. Two seedlings planted for every tree cut is a rule followed in Europe. (4) The most economical method is that shown in the lower picture on page 114, where the largest trees are thinned out over a large area so as to make room for the younger ones to grow up. The greatest dangers to the forests are from fire and from careless cutting, and these dangers may be kept in check by the efficient work of our national and state foresters.

A City's Need for Trees.--The city of Paris, well known as one of the most beautiful of European capitals, spends over $100,000 annually in caring for and replacing some of the 90,000 trees owned by the city. All over the United States the city governments are beginning to realize what European cities have long known, that trees are of great value to a city. They are now following the example of European cities by planting trees and by protecting the trees after they are planted. Thousands of city trees are annually killed by horses which gnaw the bark. This may be prevented by proper protection of the trunk by means of screens or wire guards. Chicago has appointed a city forester, who has given the following excellent reasons why trees should be planted in the city:--

(1) Trees are beautiful in form and color, inspiring a constant appreciation of nature.

(2) Trees enhance the beauty of architecture.

(3) Trees create sentiment, love of country, state, city, and home.

(4) Trees have an educational influence upon citizens of all ages, especially children.

(5) Trees encourage outdoor life.

(6) Trees purify the air.

(7) Trees cool the air in summer and radiate warmth in winter.

(8) Trees improve climate and conserve soil and moisture.

(9) Trees furnish resting places and shelter for birds.

(10) Trees increase the value of real estate.

(11) Trees protect the pavement from the heat of the sun.

(12) Trees counteract adverse conditions of city life.

Let us all try to make Arbor Day what it should be, a day for caring for and planting trees, for thus we may preserve this most important heritage of our nation.

REFERENCE BOOKS

ELEMENTARY

Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Mayne and Hatch, _High School Agriculture_. American Book
Company.
Murrill, _Shade Trees_, Bul. 205, Cornell University
Agricultural Experiment Station.
Pinchot, _A Primer of Forestry_, Division of Forestry, U. S.
Department of Agriculture.

ADVANCED

Apgar, _Trees of the United States_, Chaps. II, V, VI.
American Book Company.
Coulter, Barnes, and Cowles, _A Textbook of Botany_, Part I
and Vol. II. American Book Company.
Goebel, _Organography of Plants_, Part V. Clarendon Press.
Strasburger, Noll, Schenck, and Karston, _A Textbook of
Botany_. The Macmillan Company.
Ward, _Timber and Some of its Diseases_. The Macmillan
Company.
Yearbook, U. S. Department of Agriculture, Division of
Forestry, Buls. 7, 10, 13, 16, 17, 18, 20, 26, 27.

X. THE ECONOMIC RELATION OF GREEN PLANTS TO MAN

_Problems.--How green plants are useful to man._
_(a) As food._
_(b) For clothing._
_(c) Other uses._
_How green plants are harmful to man._

SUGGESTED LABORATORY WORK

If a commercial museum is available, a trip should be planned to work
over the topics in this chapter. The school collection may well
include most of the examples mentioned, both of useful and harmful
plants.

A study of weeds and poisonous plants should be taken up in actual
laboratory work, either by collection and identification or by
demonstration.

Green Plants have a "Dollar and Cents" Value.--To the girl or boy living in the city green plants seem to have little direct value. Although we see vegetables for sale in stores and we know that fruits have a money value, we are apt to forget that the wealth of our nation depends more upon its crops than it does on its manufactories and business houses. The economic or "dollars and cents" value of plants is enormous and far too great for us to comprehend in terms of figures.

We have already seen some of the uses to mankind of the products of the forest; let us now consider some other plant products.

Cabbage Onions Lettuce
Leaves used as food.]

Leaves as Food.--Grazing animals feed almost entirely on tender shoots or leaves, blades of grass, and other herbage. Certain leaves and buds are used by man as food. Lettuce, beet tops, kale, spinach, broccoli, are examples. A cabbage head is nothing but a big bud which has been cultivated by man. An onion is a compact budlike mass of thickened leaves which contain stored food.

Celery Kohl-rabi Potato Sugar cane
Stems used as food.]

Stems as Food.--A city child would, if asked to name some stem used as food, probably mention asparagus. We sometimes forget that one of our greatest necessities, cane sugar, comes from the stem of sugar cane. Over seventy pounds of sugar is used each year by every person in the United States. To supply the growing demand beets are now being raised for their sugar in many parts of the world, so that nearly half the total supply of sugar comes from this source. Maple sugar is a well-known commodity which is obtained by boiling the sap of sugar maple until it crystallizes. Over 16,000 tons of maple sugar is obtained every spring, Vermont producing about 40 per cent of the total output. The sago palm is another stem which supports the life of many natives in Africa. Another stem, living underground, forms one of man's staple articles of diet. This is the potato.

Roots as Food.--Roots which store food for plants form important parts of man's vegetable diet. Beets, radishes, carrots, parsnips, sweet potatoes, and many others might be mentioned.

The following table shows the proportion of foods in some of the commoner roots and stems:--

--------------------------------------------------------------------
| WATER| PROTEINS| CARBOHYDRATES| FAT | MINERAL MATTER
-------------+------+---------+--------------+-----+----------------
Potato | 75 | 1.2 | 18 | 0.3 | 1.0
Carrot | 89 | 0.5 | 5 | 0.2 | 1.0
Parsnip | 81 | 1.2 | 8.7 | 1.5 | 1.0
Turnip | 92.8 | 0.5 | 4. | 0.1 | 0.8
Onion | 91 | 1.5 | 4.8 | 0.2 | 0.5
Sweet potato | 74 | 1.5 | 20.2 | 0.1 | 1.5
Beet | 82.2 | 0.4 | 13.4 | 0.1 | 0.9
--------------------------------------------------------------------

Wheat Nuts Pear Melon
Seeds and fruits used for food.]

Fruits and Seeds as Foods.--Our cereal crops, corn, wheat, etc., have played a very great part in the civilization of man and are now of so much importance to him as food products that bread made from flour from the wheat has been called the "staff of life." Our grains are the cultivated progeny of wild grasses. Domestication of plants and animals marks epochs in the advance of civilization. The man of the stone age hunted wild beasts for food, and lived like one of them in a cave or wherever he happened to be; he was a nomad, a wanderer, with no fixed home. He may have discovered that wild roots or grains were good to eat; perhaps he stored some away for future use. Then came the idea of growing things at home instead of digging or gathering the wild fruits from the forest and plain. The tribes which first cultivated the soil made a great step in advance, for they had as a result a fixed place for habitation. The cultivation of grains and cereals gave them a store of food which could be used at times when other food was scarce. The word "cereal" (derived from Ceres, the Roman Goddess of Agriculture) shows the importance of this crop to Roman civilization. From earliest times the growing of grain and the progress of civilization have gone hand in hand. As nations have advanced in power, their dependence upon the cereal crops has been greater and greater.

"Indian corn," says John Fiske, in _The Discovery of America_, "has played a most important part in the history of the New World. It could be planted without clearing or plowing the soil. There was no need of threshing or winnowing. Sown in tilled land, it yields more than twice as much food per acre as any other kind of grain. This was of incalculable advantage to the English settlers in New England, who would have found it much harder to gain a secure foothold upon the soil if they had had to begin by preparing it for wheat or rye."

To-day, in spite of the great wealth which comes from our mineral resources, live stock, and manufactured products, the surest index of our country's prosperity is the size of the corn and wheat crop. According to the last census, the amount of capital invested in agriculture was over $20,000,000,000, while that invested in manufacture was less than one half that amount.

Corn.--About three billion bushels of corn were raised in the United States during the year 1910. This figure is so enormous that it has but little meaning to us. In the past half century our corn crop has increased over 350 per cent. Illinois and Iowa are the greatest corn-producing states, each having a yearly record of over four hundred million bushels. The figure on this page shows the principal corn-producing areas in the United States.

Indian corn is put to many uses. It is a valuable food. It contains a large proportion of starch, from which glucose (grape sugar) and alcohol are made. Machine oil and soap are made from it. The leaves and stalk are an excellent fodder; they can be made into paper and packing material. Mattresses can be stuffed with the husks. The pith is used as a protective belt placed below the water line of our huge battleships. Corn cobs are used for fuel, one hundred bushels having the fuel value of a ton of coal.

Wheat.--Wheat is the crop of next greatest importance in size. Nearly seven hundred millions of bushels were raised in this country in 1910, representing a total money value of over $700,000,000. Seventy-two per cent of all the wheat raised comes from the North Central states and California. About three fourths of the wheat crop is exported, nearly one half of it to Great Britain, thus indirectly giving employment to thousands of people on railways and steamships. Wheat has its chief use in its manufacture into flour. The germ, or young wheat plant, is sifted out during this process and made into breakfast foods. Flour making forms the chief industry of Minneapolis, Minnesota, and of several other large and wealthy cities in this country.

Other Grains.--Of the other grain and cereals raised in this country, oats are the most important crop, over one billion bushels having been produced in 1910. Barley is another grain, a staple of some of the northern countries of Europe and Asia. In this country, it is largely used in making malt for the manufacture of beer. Rye is the most important cereal crop of northern Europe, Russia, Germany, and Austro-Hungary producing over 50 per cent of the world's supply. One of the most important grain crops for the world (although relatively unimportant in the United States) is rice. The fruit of this grasslike plant, after thrashing, screening, and milling, forms the principal food of one third of the human race. Moreover, its stems furnish straw, its husks make a bran used as food for cattle, and the grain, when fermented and distilled, yields alcohol.

Garden Fruits.--Green plants and especially vegetables have come to play an important part in the dietary of man. The diseases known as scurvy and beri-beri, the latter the curse of the far Eastern navies, have been largely prevented by adding vegetables and fruit juices to the dietary of the sailors. People in this country are beginning to find that more vegetables and less meat are better than the meat diet so often used. Market gardening forms the lucrative business of many thousands of people near our great cities. Some of the more important fruits are squash, cucumbers, pumpkins, melons, tomatoes, peppers, strawberries, raspberries, and blackberries. The latter fruits bring in an annual income of $25,000,000 to our market gardeners. Beans and peas are important as foods because of their relatively large amount of protein. Canning green corn, peas, beans, and tomatoes has become an important industry.

Orchard and Other Fruits.--In the United States over one hundred and seventy-five million bushels of apples are grown every year. Pears, plums, apricots, peaches, and nectarines also form large orchards, especially in California. Nuts form one of our important articles of food, largely because of the large amount of protein contained in them.

The grape crop of the world is commercially valuable, because of the raisins and wine produced. The culture of lemons, oranges, and grapefruit has come in recent years to give a living to many people in this country as well as in other parts of the world. Figs, olives, and dates are staple foods in the Mediterranean countries and are sources of wealth to the people there, as are coconuts, bananas, and many other fruits in tropical countries.

Beverages and Condiments.--The coffee and cacao beans, and leaves of the tea plant, products of tropical regions, form the basis of very important beverages of civilized man. Pepper, black and red, mustard, allspice, nutmegs, cloves, and vanilla are all products manufactured from various fruits or seeds of tropical plants.

Alcoholic liquors are produced from various plants in different parts of the world, the dried fruit of the hop vine being an important product of New York State used in the making of beer.

Raw Materials.--Besides use as food, green plants have many other uses. Many of our city industries would not be in existence, were it not for certain plant products which furnish the raw materials for many manufacturing industries. Many cities of the east and south, for example, depend upon cotton to give employment to thousands of factory hands.

Cotton.--Of our native plant products cotton is probably of the most importance to the outside world. Over eleven million bales of five hundred pounds each are raised annually.

The cotton plant thrives in warm regions. Its commercial importance is gained because the seeds of the fruit have long filaments attached to them. Bunches of these filaments, after treatment, are easily twisted into threads from which are manufactured cotton cloth, muslin, calico, and cambric. In addition to the fiber, cottonseed oil, a substitute for olive oil, is made from the seeds, and the refuse remaining makes an excellent cattle fodder.

Cotton Boll Weevil.--The cotton crop of the United States has rather recently been threatened with destruction by a beetle called the cotton boll weevil. This insect, which bores into the young pod of the cotton, develops there, stunting the growth of the fruit to such an extent that seeds are not produced. The loss in Texas alone is estimated at over $10,000,000 a year. The boll weevil, because of the protection offered by the cotton boll, is very difficult to exterminate. The weevils are destroyed by birds, the infected bolls and stalks are burnt, millions are killed each winter by cold, other insects prey on them, but at the present time they are one of the greatest pests the south knows.

The control of this pest seems to depend upon early planting so that the crop has an opportunity to ripen before the insects in the boll grow large enough to do harm. Ultimately the boll weevil may do more good than harm by bringing into the market a type of cotton plant that ripens very early.

Vegetable Fibers.--Among the most important are Manila hemp, which comes from the leaf-stalks of a plant of the banana family and true hemp, which is the bast or woody fiber of a plant cultivated in most warm parts of the earth. Flax is also an important fiber plant, grown largely in Russia and other parts of Europe (see picture on next page). From the bast fibers of the stem of this herb linen cloth is made.

Vegetable Oils.--Some of the same plants which give fiber also produce oil. Cotton seed oil pressed from the seeds, linseed oil from the seeds of the flax plant, and coconut oil (the covering of the nut here producing the fiber) are examples.

Some Harmful Green Plants.--We have seen that on the whole green plants are useful to man. There are, however, some that are harmful. For example, the poison ivy is extremely poisonous to touch. The poison ivy is a climbing plant which attaches itself to the trees or walls by means of tiny air roots which grow out from the stem. It is distinguished from its harmless climbing neighbor, the Virginia Creeper, by the fact that its leaves are notched in _threes_ instead of _fives_. Every boy and girl should know poison ivy.

Numerous other poisonous common plants are found, but one other deserves special notice because of its presence in vacant city lots. The Jimson Weed (_Datura_) is a bushy plant, from two to five feet high, bearing large leaves. It has white or purplish flowers, and later bears a four-valved seed pod containing several hundred seeds. These plants contain a powerful poison, and people are often made seriously ill by eating the roots or other parts by mistake.

Weeds.--From the economic standpoint the green plants which do the greatest damage are weeds. Those plants which provide best for their young are usually the most successful in life's race. Plants which combine with the ability to scatter many seeds over a wide territory the additional characteristics of rapid growth, resistance to dangers of extreme cold or heat, attacks of enemies, inedibility, and peculiar adaptations to cross-pollination or self-pollination, are usually spoken of as weeds. They flourish in the sterile soil of the roadside and in the fertile soil of the garden. By means of rapid growth they kill other plants of slower growth by usurping their territory. Slow-growing plants are thus actually exterminated. Many of our common weeds have been introduced from other countries and have, through their numerous adaptations, driven out other plants which stood in their way. Such is the Russian Thistle. A single plant of this kind will give rise to over 20,000 seeds. First introduced from Russia in 1873, it spread so rapidly that in twenty years it had appeared as a common weed over an area of some twenty-five thousand square miles. It is now one of the greatest pests in our Northwest.

REFERENCE BOOKS

ELEMENTARY

Hunter, _Laboratory Problems in Civic Biology_. American
Book Company.
Gannet, _Commercial Geography_. American Book Company.
Sargent, _Plants and their Uses_. Henry Holt and Company.
Toothaker, _Commercial Raw Materials_. Ginn and Company.
U. S. Dept. of Agriculture, Farmers' Bulletin 86, _Thirty
Poisonous Plants of the United States_, V. K. Chestnut.
Bulletin 17. _Two Hundred Weeds, How to Know Them and How to
Kill Them_, L. H. Dewey.

ADVANCED

Bailey, _Cyclopedia of American Agriculture_. The Macmillan
Company.

XI. PLANTS WITHOUT CHLOROPHYLL IN THEIR RELATION TO MAN

_Problems.--(a) How molds and other saprophytic fungi do harm to man._
_(b) What yeasts do for mankind._
_(c) A study of bacteria with reference to_
_(1) Conditions favorable and unfavorable to growth._
_(2) Their relations to mankind._
_(3) Some methods of fighting harmful bacteria and diseases
caused by them._

LABORATORY SUGGESTIONS

_Field work._--Presence of bracket fungi and chestnut
canker.
_Home experiment._--Conditions favorable to growth of mold.
_Laboratory demonstration._--Growth of mold, structure,
drawing.
_Home experiment or laboratory demonstration._--Conditions
unfavorable for growth of molds.
_Demonstration._--Process of fermentation.
_Microscopic demonstration._--Growing yeast cells. Drawing.
_Home experiment._--Conditions favorable for growth of
yeast.
_Home experiment._--Conditions favorable for growth of yeast
in bread.
_Demonstration and experiment._--Where bacteria may be
found.
_Demonstration._--Methods of growth of bacteria, pure
cultures and colonies shown.
_Demonstration._--Foods preferred by bacteria.
_Demonstration._--Conditions favorable for growth of
bacteria.
_Demonstration._--Conditions unfavorable for growth of
bacteria.
_Demonstration by charts, diagrams, etc._--The relation of
bacteria to disease in a large city.

COLORLESS PLANTS ARE USEFUL AND HARMFUL TO MAN

The Fungi.--We have found that green plants on the whole are useful to mankind. But not all plants are green. Most of us are familiar with the edible mushroom sold in the markets or the so-called "toadstools" found in parks or lawns. These plants contain no chlorophyll and hence do not make their own food. They are members of the plant group called _fungi_. Such plants are almost as much dependent upon the green plants for food as are animals. But the fungi require for the most part dead organic matter for their food. This may be obtained from decayed vegetable or animal material in soil, from the bodies of dead plants and animals, or even from foods prepared for man. Fungi which feed upon _dead_ organic material are known as _saprophytes_. Examples are the mushrooms, the yeasts, molds, and some bacteria, of which more will be learned later.

Some Parasitic Fungi.--Other fungi (and we will find this applies to some animals as well) prefer _living_ plants or animals for their food. Thus a tiny plant, recently introduced into this country, known as the chestnut canker, is killing our chestnut trees by the thousands in the eastern part of the United States. It produces millions of tiny reproductive cells known as _spores_; these spores, blown about by the wind, light on the trees, sprout, and send in under the bark a threadlike structure which sucks in the food circulating in the living cells, eventually causing the death of the tree. _A plant or animal which lives at the expense of another living plant or animal is called a parasite._ The chestnut canker is a dangerous parasite. Later we shall see that animal and plant parasites destroy yearly crops and trees valued at hundreds of millions of dollars and cause untold misery and suffering to humanity.

Another fungus which does much harm to the few trees found in large towns and cities is the shelf or bracket fungus. The part of the body visible on the tree looks like a shelf or bracket, hence the name. This bracket is in reality the reproductive part of the plant; on its lower surface are formed millions of little bodies called _spores_. These spores are capable, under favorable conditions, of reproducing new plants. The true body of the plant, a network of threads, is found under the bark. This fungus begins its life as a spore in some part of the tree which has become _diseased_ or _broken_. Once established, it spreads rapidly. There is no remedy except to kill the tree and burn it, so as to destroy the spores. Many fine trees, sound except for a slight bruise or other injury, are annually infected and eventually killed. In cities thousands of trees become infected through careless hitching of horses so that the horse may gnaw the tree, thus exposing a fresh surface on which spores may obtain lodgment and grow (see page 115).

Suggestions for Field Work.--A field trip to a park or grove near home may show the great destruction of timber by this means. Count the number of perfect trees in a given area. Compare it with the number of trees attacked by the fungus. Does the fungus appear to be transmitted from one tree to another near at hand? In how many instances can you discover the point where the fungus first attacked the tree?

Fungi of our Homes.--But not all fungi are wild. Some have become introduced into our homes and these live on food or other materials. _These plants are very important because of their relation to life in a town or crowded city._[17]

Footnote 17: Experiments on conditions favorable to growth
of mold should be introduced here.

The Growth of Bread Mold.--If a piece of moist bread is exposed to the air of the schoolroom, or in your own kitchen for a few minutes and then covered with a glass tumbler and kept in a warm place, in a day or two a fuzzy whitish growth will appear on the surface of the bread. This growth shortly turns black. If we now examine a little piece of the bread with a lens or low-powered microscope, we find a tangled mass of threads (the _mycelium_) covering the surface of the bread. From this mass of threads project tiny upright stalks bearing round black bodies, the fruit. Little rootlike structures known as _rhizoids_ dip down into the bread, and absorb food for its threadlike body. The upright threads with the balls at the end contain many tiny bodies called _spores_. These spores have been formed by the division of the protoplasm making up the fruiting bodies into many separate cells. When grown under favorable conditions, the spores will produce more mycelia, which in turn bear fruiting bodies.

Physiology of the Growth of Mold.--Molds, in order to grow rapidly, need oxygen, moisture, and moderate heat. They seem to prefer dark, damp places where there is not a free circulation of air, for if the bell jar is removed from growing mold for even a short time, the mold wilts. Too great or very little heat will prevent growth and kill everything except the spores. They obtain their food from the material on which they live. This they are able to do by means of digestive enzymes given out by the rootlike parts, by means of which the molds cling to the bread. These digestive enzymes change the starch of the bread to sugar and the protein to a soluble form which will pass by osmosis into cells of the mold. Thus the mold is able to absorb food material. These foods are then used to supply energy and make protoplasm. This seems to be the usual method by which saprophytes make use of the materials on which they live.

What can Molds live On?--We have seen that black mold lives upon bread. We would find that it or some other mold (_e.g._ green or blue mold) live upon decaying or overripe fruit,--apples, peaches, and plums being especially susceptible to their growth. Molds feed upon all cakes or breads, upon meat, cheese, and many raw vegetables. They are almost sure to grow upon flour if it is allowed to get damp. Moisture seems necessary for their growth. Jelly is a substance particularly favorable to molds for this reason. Shoes, leather, cloth, paper, or even moist wood will give food enough to support their growth. At least one troublesome disease, _ringworm_, is due to the growth of molds in the skin.

What Mold does to Foods.--Mold usually changes the taste of the material it grows upon, rendering it "musty" and sometimes unfit to eat. Eventually it will spoil food completely because decay sets in. Decay, as we will see later, is not entirely due to mold growth, but is usually caused by another group of organisms, the _bacteria_. Molds, however, in feeding _do_ cause chemical changes which result in decay or putrefaction. Some molds are useful. They give the flavor to Roquefort, Gorgonzola, Camembert, and Brie cheeses. But on the whole molds are pests which the housekeeper wishes to get rid of.

How to prevent Molds.[18]--As we have seen, moisture is favorable for mold growth; conversely, dryness is unfavorable. Inasmuch as the spores of mold abound in the air, materials which cannot be kept dry should be covered. Jelly after it is made should at once be tightly covered with a thin layer of paraffin, which excludes the air and possible mold spores. Or waxed paper may be fastened over the surface of the jelly so as to exclude the spores. To prevent molds from attacking fresh fruit, the surface of the fruit should be kept dry and, if possible, each piece of fruit should be wrapped in paper. Why? Heating with dry heat to 212 deg. for a few moments will kill any mold spores that happen to be in food. Moldy food, if heated after removing surface on which the mold grew, is perfectly good to eat.

Footnote 18: An experiment to show conditions unfavorable
for growth of molds should be shown at this point.

Dry dusting or sweeping will raise dust, which usually contains mold spores. Use a dampened broom or dust cloth frequently in the kitchen if you wish to preserve foods from molds.

Other Moldlike Fungi.--Mildews are near relatives of the molds found in our homes. They may attack leather, cloth, etc., in a damp house. Other allied forms may do damage to living plants. Some of these live upon the lilac, rose, or willow. These fungi do not penetrate the host plant to any depth, for they obtain their food from the outer layer of cells in the leaf of their host and cover the leaves with the whitish threads of the mycelium. Hence they may be killed by means of applications of some fungus-killing fluid, as Bordeaux mixture.[19] Among the useful plants preyed upon by mildews are the plum, cherry, and peach trees. (The diseases known as black knot and peach curl are thus caused.) Another important member of this group is the tiny parasite found on rye and other grains, which gives us the drug ergot.

Footnote 19: See Goff and Mayne, _First Principles of
Agriculture_, page 59, for formula of Bordeaux mixture.

Among other parasitic fungi are rusts and smuts. Wheat rust is probably the most destructive parasitic fungus. Indirectly this parasite is of considerable importance to the citizen of a great city because of its effect upon the price of wheat.

YEASTS IN THEIR RELATION TO MAN

Fermentation.--It is of common knowledge to country boys or girls that the juice of fresh apples, grapes, and some other fruits, if allowed to stand exposed to the air for a short time will _ferment_. That is, the sweet juice will begin to taste sour and to have a peculiar odor, which we recognize as that of alcohol. The fermenting juice appears to be full of bubbles which rise to the surface. If we collect enough of these bubbles of gas to make a test, we find it to be carbon dioxide.

Evidently something changed some part of the apple or grape, the sugar, (C{6}H{12}O{6}), into alcohol, 2(C{2}H{6}O), and carbon dioxide, 2(CO{2}). This chemical process is known as _fermentation_.

Yeast causes Fermentation.--Let us now take a compressed yeast cake, shake up a small portion of it in a solution of molasses and water, and fill a fermentation tube with the mixture. Leave the tube in a warm place overnight. In the morning a gas will be found to have been collected in the closed end of the tube (see Figure on page 138). The taste and odor of the liquid shows alcohol to be present, and the gas, if tested, is proven carbon dioxide. Evidently yeast causes fermentation.

What are Yeasts?--If now part of the liquid from the fermentation tube which contains the settlings be drawn off, a drop placed on a slide and a little weak iodine added and the mixture examined under the compound microscope, two kinds of structures will be found (see Figure below), starch grains which are stained deep blue, and other smaller ovoid structures of a brownish yellow color. The latter are yeast plants.

Size and Shape, Manner of Growth, etc.--The common compressed yeast cake contains millions of these tiny plants. In its simplest form a yeast plant is a single cell. The shape of such a plant is ovoid, each cell showing under the microscope the granular appearance of the protoplasm of which it is formed. Look for tiny clear areas in the cells; these are vacuoles, or spaces filled with fluid. The nucleus is hard to find in a yeast cell. Many of the cells seem to have others attached to them, sometimes there being several in a row. Yeast cells reproduce very rapidly by a process of budding, a part of the parent cell forming one or more smaller daughter cells which eventually become free from the parent.

Conditions favorable to growth of Yeast.--_Experiment._--Label three pint fruit jars A, B, and C. Add one fourth of a compressed yeast cake to two cups of water containing two tablespoonfuls of molasses or sugar. Stir the mixture well and divide it into three equal parts and pour them into the jars. Place covers on the jars. Put jar A in the ice box on the ice, and jar B over the kitchen stove or near a radiator; pour the contents of jar C into a small pan and boil for a few minutes. Pour back into C, cover and place it next to B. After forty-eight hours, look to see if any bubbles have made their appearance in any of the jars. If the experiment has been successful, only jar B will show bubbles. After bubbles have begun to appear at the surface, the fluid in jar B will be found to have a sour taste and will smell unpleasantly. The gas which rises to the surface, if collected and tested, will be found to be carbon dioxide. The contents of jar B have fermented. Evidently, the growth of yeast will take place only under conditions of moderate warmth and moisture.