THE LEAF. 



205 



tion of the foliar organ by means of facial fission; and 

 it will be seen that the following interpretation will 

 clear np and explain many a bizarre and otherwise 

 inexplicable " freak." 



No instance seems to be known in which facial fission 

 has resulted in the formation of two perfectly distinct 

 leaves, but the case of the double vine-leaf described 

 above is a near approach thereto in which attach- 

 ment obtains by the leaf-stalk only. Then come the 

 cases of the mango, the tobacco-leaf, and those of 

 Buddleia, in which the attachment between the two 

 leaves extends for a long distance, or the whole way, 

 along the midribs. This is precisely the condition, 

 and the same structure, which we see in the virescent 

 stamens in which a green lamina is developed along 

 either side of the midrib on the ventral surface of the 

 anther, and which, save for its inverse orientation, 

 resembles exactly the normally-orientated virescent 

 portion. 



The next stage is seen in the case of the Polygonum- 

 and P//te-leaves, and some of those of the saxifrage, 

 and normally in some species of Oaltha, in which the 

 ventral or dorsal laminae extend only part way along 

 the midrib, or never meet above to form an indivi- 

 dualized ventral blade, or are very poorly developed 

 as compared with the leaf which bears them. Such 

 laminae may extend along some of the lateral veins or 

 may unite with the basal margins of the leaf to form 

 pockets. Or, again, a transition may occur, as in the 

 saxifrage, between such a case with two basal pockets 

 and the fusion of these to form a single large basal 

 pocket ; here the ventral laminae, which are basally 

 united with the leaf -margins, extend only a short way 

 up the midrib and unite together across it ; or we can 

 picture it more easily, perhaps, by imagining the mid- 

 rib of the basal pocket of a leaf to become united for 

 a certain distance with the main midrib of the latter, 

 which is the reverse process. In fact, there exists, as 

 is specially well seen in the saxifrage-leaves above 



