72 UNIVERSALITY OF DEGENERATIVE EVOLUTION 



creasing in size, decrease in number. At first there 

 may be three leaflets, and then only a single large 

 leaflet (fig. 38, G). 

 Finally, towards the 

 floral end of the 

 branch the leaflet be- 

 comes smaller and 

 smaller until it dis- 

 appears altogether 

 (fig. 38, H and i). 

 The apical leaves, like 

 the basilar leaves, are 

 eventually reduced 

 simply to the hypopod. 



2. Serratula cen- 

 tauroides.ThQ foli- 

 age leaves of this 

 species are close to 

 the ground, their bases 

 are ensheathed, and 

 the long petioles ter- 

 minate in rhomboidal 

 blades. 



In passing on from 

 these assimilative 

 leaves to the basilar 

 and apical leaves, a 

 double adaptation becomes apparent, as in Rosa 

 rugosa. In Rosa rugosa, however, both adaptations 

 were protective, while in Serratula centauroides this 



closing the swollen portion and ro led leaves 

 protecting the bud ; B,C, submerged leaves; 

 D,E, floating leaves; F, aerial foliage leaf; 

 G, leaf protecting the flower-bud ; H, 

 seedling grown from a seed planted in the 

 water on the surface of the mud. I, seed- 

 ling from seed planted in the water under 

 a layer of mud. In figures H and I, c is 

 the cotyledon, I the first leaves. 



