220 OF THE FULCRA, 



■just above their insertion. The Europaean 

 RubiacecB have whorled leaves, as Aspe- 

 rula, Galium, Rubia, Sec; but Asperula 

 cynanchica, Engl. Bot. t. 33, has some- 

 times two of its four leaves so small as to 

 look like stipulas, seeming to form an inter- 

 mediate link between such as have whorled 

 leaves and such as have opposite ones with 

 stipulas. The next step from Asperula is 

 Diodia, and then Spermacoce. In the 

 two last the bases of the stipulas and foot- 

 stalks are united into a common tube. 



Some stipulas fall off almost as soon as 



the leaves are expanded, which is the case 



with the Tulip-tree,' Liriodendron tulipi- 



fera ; in general they last as long as the 



leaves. 



The absence or presence of these organs, 

 though generally an indication that plants 

 belong to the same natural order and even 

 genus, is not invariably so. Some species 

 of Cistus have stipulas, others none, which 

 is nearly the case with grasses. The 

 stipula in this, one of the most distinct 

 of all natural orders, is peculiar, consisting 

 of an internal white membrane crowning 



