690 



PART IV. THE PHYSIOLOGY OF PLANTS. 



Sensitiveness to long-continued contact is manifested by the 

 petioles of various plants (e.g. Tropaeolum, Clematis) ; sometimes 



A B 



FIG. 472 (after Duchartre) . Leaves of Mimosa pudica: A normal diurnal position; 

 B position assumed on stimulation. 



by the whole phyllopodium (Lygodium) ; in many cases leaves 

 possessing this sensitiveness are modified into leaf -tendrils (see p., 



58 ; as in Cucurbitacese, etc.) ; 

 leaves of this kind serve as 

 organs of attachment for climb- 

 ing. 



Foliage-leaves are sometimes 

 modified into pitchers or ascidia 

 (p. 57) : these serve the purpose 

 in some cases (e.g. Nepenthes) 

 of capturing insects and of 

 digesting and absorbing them : 

 in other cases (e.g. Dischidia) 

 they collect water and organic 

 detritus ; in Dischidia adven- 

 titious roots are developed, 

 which lie in the pitchers and 

 absorb water, together with 

 dissolved substances, there- 

 from. 



Leaf-spines appear to be exclusively protective against the 

 attacks of herbivorous animals. 



FIG. 473 (after Darwin). Petiole of Solanum 

 jasminoides clasping a stick. 



