36 BUDS AND STIPULES 



protecting it. So, also, in the other exstipulate species 

 the leaf-stalks are all more or less widened at the base, 

 and the bud is thus protected. 



On the other hand, our common Helianthemum (H. 

 vulcjare) (fig. 22) has the leaf-stalk narrowed at the base, 

 and glabrous or nearly so. The bud, therefore, would 

 be exposed if it were not for the stipules. So, also, in 

 the other species which have stipules the leaf-stalks are 

 narrowed at the base, and the buds are protected by the 

 stipules. 



Hence we have a very strong presumption that the 

 answer to Vaucher's problem is that some species of 

 Helianthemum have stipules in order to protect the 

 bads ; and that in others, where this function is per- 

 formed by the dilated bases of the leaf-stalk, stipules 

 would be unnecessary, and do not occur. 



Helianthemum c/uttatum is particularly interesting 

 in this respect. The upper leaves have stipules, while 

 the lower ones have none. Now the lower leaves have 

 broad leaf-bases, which effectually protect the bud, and 

 they are exstipulate ; the upper leaves, on the contrary, 

 are narrow at the base, but they are provided with 

 stipules. 



The reason for the presence or absence of stipules 

 seems, then, quite obvious, so far as the Rock Roses 

 (Helianthemum) are concerned. 



Let us now see whether the conformation of other 

 species supports this view. In the allied genus Cistus, 



