4 INTRODUCTION TO BOTANY 



condition. In the case of some of these domesticated plants 

 for example, wheat it is possible that a single wild plant 

 may have produced as much and as good wheat as one cul- 

 tivated plant does now, but in most cases, doubtless, great 

 improvements have been made, and in all cases the total 

 product has been vastly increased. The northwestern United 

 States produces wheat that is of great importance to the wel- 

 fare of the nation. In the corn belt of the central United 

 States there are seven states that produce nearly half the 

 corn used in the whole world an amount that is ordinarily 

 worth annually almost three billion dollars. The cotton crop 

 of the Southern states (three fifths of the cotton of the world), 

 together with cotton-seed products, is worth annually nearly 

 one billion dollars. 



3. Plants are everywhere. Cultivated plants constitute only 

 a very small part of the plant population of the earth. In fact, 

 we are so accustomed to seeing plant life on every hand that 

 we ordinarily think little about it. Most people have never 

 been in surroundings where plant life is not fairly abundant. 

 The upper parts of the cones of active volcanoes and the in- 

 teriors of their craters, a few mud volcanoes and hot springs, 

 the exposed surfaces of arctic ice fields or of glaciers, together 

 with a few poisonous alkali tracts, are almost the only parts 

 of the earth's surface on which or in which plant life is 

 not present. There are, however, very great differences in the 

 density of the plant population of different regions. Many 

 deserts have only here and there a shrub or other plant capa- 

 ble of enduring the inhospitable soil and climatic conditions 

 there encountered. In the sand hills which are found along 

 the Great Lakes (fig. 1), along the shores of the Atlantic 

 Ocean, and elsewhere few plants are able to grow. On the 

 other hand, a weedy garden, a grass lawn, or a meadow usually 

 has hundreds of plants to every square yard of surface, and 

 tropical forests often present a tangled mass of vegetation 

 (fig. 2) towering up to a height of nearly two hundred feet, 

 interlaced with climbing plants, sometimes hundreds of feet 



