PART IV 



THE KINDS OF PLANTS 



Number of Plants. — Above 120,000 distinct kinds or 

 species of seed-bearing plants are known and described. 

 Probably little more than one-half of the total number now- 

 existing on the earth is known. Even in the older countries 

 and regions, seed-bearing plants heretofore unknown to 

 science are discovered now and then. Outlying regions 

 are relatively little known botanically. Large parts of 

 Africa, South America, Central America, China, Central 

 Asia, and the tropical islands are only imperfectly explored 

 for plants. Cryptogamous plants are very numerous in 

 kinds, and many kinds — as, for example, various bacteria 

 — are almost infinite in numbers of individuals. In the 

 lower ranges of cryptogamous plants, as in fungi and bac- 

 teria, new kinds are being described even in countries in 

 which they have been carefully studied. 



Species. — Each kind of plant is called a species. There 

 is no absolute mark or characteristic of a species. Between 

 many kinds there are intermediate forms, and some kinds 

 vary immensely under different conditions. What one 

 botanist considers as a distinct species another botanist 

 may regard as only a variety or form of another species. 

 No two botanists agree as to the number of species in any 

 region. Species are not things in themselves. In practice, 

 any kind of plant that is distinct enough to be recognized 

 by a description, and that is fairly constant over a con- 

 siderable territory, is called a species. We make species 

 merely to enable us to talk and to write about plants: we 

 must have names to call them by. The different kinds of 

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