*70 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



by degeneration. A good demonstration of this will 

 be to examine the leaves of the following types : 

 Rosa rugosa, Serratula centauroides, Sagittaria sagitti- 

 folia, Lathyrus Aphaca, and NympJiaea dentata. 1 



1. Rosa rugosa. In the foliage leaves (fig. 38, F) 

 of a rose-branch, such as of Rosa rugosa, there are two 



Fig. 38. Leaves from the same branch of Rosa rugosa. 

 A E, successive basilar leaves ; F, foliage leaf; G I, successive apical leaves. 



lateral stipules which arise from the hypopod and 

 are fused with the base of the petiole. The petiole, 

 which arises from the mesopod, has from two to six 

 pairs of leaflets, and also a terminal leaflet all of 

 which are derived from the epipod. 



1 In studying these types we will confine our attention to the 

 leaves arising directly from the foliage leaves, to the exclusion of 

 the floral leaves. 



