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 temperaturp 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 volcanic 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 weU 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 hving organisms. Many plants are so 



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