PART IV 

 THE KINDS OF PLANTS 



NUMBER OF PLANTS.— Above 125,000 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 are known. Even in the older coun- 

 tries and regions, seed -bearing plants heretofore unknown 

 to science are discovered now and then. Outlying regions 

 are relatively little known botanically. The larger part 

 of Africa, South America, Central America, China, Cen- 

 tral Asia, and the tropical islands are only imperfectly 

 explored for plants. Crjptogamous plants are far more 

 numerous in kinds than seed- plants, and many kinds — as, 

 for example, various bacteria — are almost infinite in 

 numbers of individuals. In the lower ranges of cryptog- 

 amous plants, as in fungi and bacteria, many new kinds 

 are constantly being described even in countries in which 

 they have been most 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 them- 

 selves. In practice, any kind of plant which is distinct 

 enough to be recognized by a description, and which is 

 fairly constant over a considerable territory, is called a 

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