CHAPTER II 
A GENERAL VIEW OF PLANTS 
Abundance and Distribution of Plants. — Plants are so abun- 
dant and generally distributed that there are very few regions 
that do not have plants. Plants occur in the water and in the 
soil as well as on the surface of the earth. Some plants live in 
the bodies of animals. Some are able to live where the tem- 
perature is intensely cold, while others can live in hot springs 
where the temperature is not far from the boiling point. Even 
on rocks that look quite bare, a close examination will show that 
some plant forms are present. Only in exceptional places, such 
as voleanic regions, some hot springs, and regions of salt deposits, 
are plants generally absent. 
The abundance or scarcity of plants in a given region depends 
upon how well the conditions of the region meet the requirements 
for plant growth. If the soil is dry, as in desert regions, the 
average number of plants per area is usually quite small, while in 
regions where there is sufficient moisture and sufficient mineral 
substances, more than 100,000 plants may occur on an area no 
larger than an average garden. However, the number of plants 
which can occur on a given area, is often very different from the 
number that can do well on this same area. Many more grain 
plants can be grown per acre than are grown, but agriculturists 
have learned that only a limited number of plants per acre can 
do well. Among plants, as among animals, there is competition. 
Plants must compete with each other for moisture, mineral 
substances, and sunlight, and when the competition is too great, 
as occurs when plants are too much crowded, some or all of the 
plants suffer and fail to produce good yields. By controlling 
the amount of seed sown and by properly distributing the seed, 
the farmer is able to raise the greatest number of plants per acre 
with the least loss from competition among the plants. 
Diversity of Plant Forms. — Plants are not only the smallest, 
but also the largest of living organisms. Many plants are so 
5 
