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 
