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HEREDITY AND EVOLUTION IN PLANTS 



2. Lamarck's Hypothesis. The noted French naturalist, 

 Lamarck, taught that all living things have been derived 

 from preexisting forms; that the effects of use and disuse 

 caused changes in bodily structure; that these changes 

 were inherited and accentuated from generation to genera- 

 tion; that, being of use, those individuals possessing the 

 changes in greatest perfection survived, while others per- 



FIG. 46. Water buttercup (Ranunculus aquatilis), showing aerial 

 leaves (a), and aquatic leaves (w). /, fruit. Drawn from herbarium 

 specimen. 



ished; and that the derivation of new species is thus ac- 

 counted for in a simple and logical manner. By continual 

 reaching for tender leaves on high branches, the long neck 

 of the giraffe was gradually produced, the slight gain in 

 length in one generation being transmitted by inheritance 

 to the next, and so on. 



The main thesis of Lamarck, as stated by himself, is 

 as follows: 



