88 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



the ants live and obtain nutriment, not only at the 



ends of the leaflets, but also in a thorny gland which 



is situated upon the petiole. 



5. Adaptation to drought. 

 In places where rain 

 seldom falls, plants are 

 provided with natural 

 reservoirs of water. These 

 reservoirs are situated 

 either in the roots or the 

 stems and occasionally in 

 the leaves. Where the 

 leaves are fleshy, these 

 reservoir leaves are gener- 

 ally very simple in forma- 

 tion. Those of Sempervi- 

 vum and of several other 



genera arise directly from the primordial, non- 

 differentiated leaf, 



and there is no 



differentiation into 



hypopod, epipod 



and petiole (fig. 



49). See further 



on (fig. 73), p. 236 



(Sempervivum tec- 



tOTU r ffi] ^ IG< k Branch of Caragana. 



6. Adaptation to defence against herbivorous 

 animals. Thorns are an adaptation which serve as 

 a protection against herbivorous animals. They 



FIG. 49. Growing point of Semper- 

 vivum arachnoideum. 



