CHAP, v.] ROOT-ADAPTATIONS 39 



as will be described below ; but they may 

 become so fixed as to be hereditary and then 

 appear in anticipation of their use. 



I have mentioned the ivy. This often supplies 

 a good illustration both of direct adaptation 

 and heredity of an acquired character. If any 

 shoot happens to creep along the ground, it 

 develops ordinary roots which penetrate the soil 

 for nourishment. But if it touch a wall or 

 tree-trunk, it develops quite different roots 

 adapted for climbing. Here, then, we have two 

 results of immediate response to two different 

 conditions. That the latter kind of roots can 

 be hereditary as well, is seen in the fact that 

 when shoots hang down in a shady place without 

 touching a wall, they often have rudimentary 

 roots, as if ready to be fixed upon a wall if it 

 could find one. 



But this is by no means a unique example. 

 Strawberry runners root at the joints for pro- 

 pagative purposes, the formation of roots being 

 a universal result of the presence of a damp 

 soil ; but if a young runner be trained to grow 

 erect up a stick, roots make their appearance but 

 cannot develop properly in the air. Hence the 

 " stages of acquirements " may be stated thus : 

 First, the " direct action " of the environment 

 calls out the responsive power in the plant, and 

 it develops the appropriate structure. If the 

 influence be continued long enough, i.e., through 



