ADAPTATION 



379 



the term in its widest sense, owe their lack of vigour partly to 

 adverse environmental conditions and partly to inherited char- 

 acteristics. Just as a human being with a " weak constitution " 

 may have inherited his defect or owe it to the surroundings in 

 which he grows up. 



Unlike most animals, plants cannot choose their place of 

 habitation. The seeds or spores are carried passively to a 

 variety of situations, and their chances of developing into mature 



FIG. 221. Alpine (A.) and lowland (L.) forms of the Rock Rose (Helian- 

 themum vulgare). (After Bonnier.) 



plants depend upon their power of accommodating themselves 

 to the environment in which they may be placed. But many 

 plants exhibit this power of adaptation to a very marked degree, 

 as is well illustrated by those aquatics which can grow either 

 totally submerged or on exposed mud (cf. p. 175), by the sun- 

 and-shade-forms of woodland plants (p. 168), and by the Alpine 

 forms of lowland plants (p. 170, Fig. 221). 



It has long been a matter of dispute as to whether or no 

 the changes, impressed upon an organism by the environment, 

 bring about any corresponding internal modification by means 



