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A mesophytic condition. A valley in central New York.

of the ground is frozen, thus preventing water from finding its way below the surface.

Plant Societies. Field Work. Any boy or girl who has access to a vacant lot or city park can easily see that plants group themselves into societies. Certain plants live together because they are adapted to meet certain conditions. Societies of plants exist along the dusty edge of the roadside, under the trees of the forest, along the edge of the brook, in a swamp or a pond. It should be the aim of the field trips to learn the names of plants which thus associate themselves and the conditions under which they live, and especially their adaptations to the given conditions.1

OTHER FACTORS.-It is a matter of common knowledge that plants in different regions of the earth differ greatly from one another in shape, size, and general appearance. If we study the causes for these changes, it becomes evident that the very same factors which govern hydrophytic, xerophytic, and mesophytic conditions determine, at least in part, the habits of the plants growing in a given region be it in the tropics or arctic regions. But in addition to water supply the factors of temperature, light, soil, wind, etc., all play important parts in determining the form and structure of a plant.

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1 Suggestions for such excursions are found in Andrews, Botany all the Year Round, Lloyd and Bigelow, The Teaching of Biology, Ganong, The Teaching Botanist, and many other books. A convenient form of excursion is found in Hunter and Valentine, Manual, page 202.

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size of plants decreases as we approach the line of perpetual snow. The largest trees occur at the base of the mountains; the same species of trees near the summit appear as mere shrubs. Continued cold and high winds are evidently the factors which most influence the slow growth and the size and shape of plants near the mountain tops. Cold, little light during the short days of the long winter, and a slight amount of moisture all act upon the vegetation of the arctic region, tending toward very slow growth and dwarfed and stunted form. Trees over five hundred years old have been noted in cold regions with trunks less than three feet in diameter at the base.


Conditions in a moist, semi-tropical forest. The so-called "Florida moss " is a flowering plant. Notice the resurrection ferns on the tree trunk.

VEGETATION OF THE TROPICS.- A rank and luxuriant growth is found in tropical countries with a uniformly high temperature and large rainfall. In general it may be estimated that the rainfall in such countries is at least twice as great as that of New York state, and in many cases three to four times as great. An abundant water supply, together with an average temperature of over 80° Fahrenheit, causes extremely rapid growth. One of the bamboo family, the growth of which was measured daily, was found to increase in length on the average nearly three inches in the daytime and over five inches during each night. The moisture present in the atmosphere allows of the growth of many air plants (epiphytes), which take the moisture directly from the air by means of aërial roots.

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The absence of cold weather in tropical countries allows trees to mature without a thick coating of bark or corky material. The trees all have a green and fresh appearance. Monocotyledonous plants prevail. Ferns of all varieties, especially the largest tree ferns, are abundant.

PLANT LIFE IN THE TEMPERATE ZONES.-In the state of New York conditions are those of a typical temperate flora. Extremes of cold and heat are found, the temperature ranging from 30° Fahrenheit below zero in the winter to 100° or over in the summer. Conditions of moisture show an average rainfall of from 60 to 130 cm. Conditions of moisture in the country cause great differences in the plant covering.

In the eastern part of the United States the rainfall is sufficient to give foothold to great forests, which aid in keeping the water in the soil. In the middle West the rainfall is less, the prairies are covered with grasses and other plants which have become adapted to withstand dryness. In the desert region of the Southwest we find true xerophytes, cacti, switch plants, yuccas, and others, all plants which are adapted to withstand almost total absence of moisture. In the temperate zone the water supply is the primary factor which determines the form of plant growth.



Andrews, Botany All the Year Round. American Book Company.
Leavitt, Outlines of Botany. American Book Company.
Coulter, Plant Relations. D. Appleton and Company.
Stevens, Introduction to Botany. D. C. Heath and Company.


Bailey, The Survival of the Unlike. The Macmillan Company.
Darwin, Animals and Plants under Domestication, Chaps. IX, XII. D. Appleton

and Company.

Kerner. Natural History of Plants. 4 Vols. Henry Holt and Company.
Schimper, Plant Geography. Clarendon Press.

Year Book, Department of Agriculture, 1894, 1895, 1898, 1900.



SYSTEMATIC BOTANY. -The plant world is divided into many tribes or groups. Any one who has visited a hothouse or a large garden is likely to notice this fact. And not only are plants placed in large groups which have some very conspicuous characters in common, but smaller groupings can be made in which perhaps only a few plants having common characters may be placed. If we plant a number of peas so that they will all germinate under the same conditions of soil, temperature, and sunlight, the seedlings that develop will each differ one from another in a slight degree. But in a general way they will have many characters in common, as the shape of the leaves, the possession of tendrils, form of the flower and fruit. The smallest group of plants or animals having certain characters in common that make them different from all other plants or animals is called a species. Individuals of such species may differ slightly; indeed no two individuals are exactly alike. It is known that in some cases seeds from plants which have thus varied to a considerable degree may reproduce these variations in the young plants. This fact is made use of by plant breeders to produce new kinds of plants.

Species are grouped together in a larger group called a genus. For example many kinds of peas - the everlasting pea, the wild beach peas, the sweet peas, and many others—are all grouped in one genus (called Lathyrus or vetchling) because they have certain structural characteristics in common.

NOMENCLATURE. When we wish to identify a plant, we look it up by means of its generic and specific names in much the same way that we look up a name in a city directory. As in a directory the last name of the person is placed first, as Jones, John, so we find the Latin name Phaseolus given to the beans as a genus. Phaseolus vulgaris is the name of the common bean; Phaseolus lunatus, the pole or lima bean; and Phaseolus multiflorus, the scarlet runner.

SYSTEM OF CLASSIFICATION ARTIFICIAL. Plant and animal genera are brought together in still larger groups, the classification based on general likenesses in structure. Such groups are called, as they become successively larger, Family or Tribe, Order, and Class. Thus the whole plant and animal kingdom is artificially massed in separate divisions, the smallest of which contains a few individuals very much alike; and the largest of which contains very many groups of individuals, the groups having some characters in common. This is called a system of classification.

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