3] 



PHYSIOLOGICAL REACTIONS 



89 





Fig. 22. — Various adaptations for climbing, twining, scrambling, and running. 

 A ( X \), leaf-tendrils of Common Pea {Pisiim sativum, left) and Clematis (Clematis 

 sp., right); B, branches of Bougainvillaea modified as spines used in scrambling 

 ( ■; I); C, Dodder (Cuscuta), a parasitic twiner that sends haustoria into the host- 

 plant (:, i); D, a ' Walking ' Fern (Adiaiituin caudatum) ( :< -3); E, Ivy {Hedera), 

 showing climbing roots ( X -j). 



in response to the particular conditions under which it has grown. 

 Thus in the latter instance we may even get large but thin ' shade ' 

 leaves and small but thick ' sun ' leaves on the selfsame branch of 

 a tree, whereas no matter under what conditions most compact 

 desert plants are grown they will not become tall and lax, the char- 

 acteristic of compactness being in such instances usually hereditary 



