62 THE STRUCTURE OF FLOWERS. 



CHAPTER VII. 



THE PRINCIPLE OF COHESION — Continued. ' 



Cohesion of Carpels, or Syncarpous Pistil. — The accepted ■ 

 doctrine that the carpels are metamorphosed leaves, will be 

 considered more fully when teratological modifications 

 come to be discussed ; and the proof that an ordinary 

 carpel, such as a legume, is merely a leaf folded npon itself 

 in a conduplicate manner with the margins coalescing and 

 then metamorphosed into a new organ, requires no special 

 evidence now. That a syncarpous pistil consists of two or 

 more carpellary leaves coalescing is equally admitted ; and 

 there are two methods of cohesion. Either the carpels may 

 be ab initio composed of unclosed leaves, which cohere by their 

 edges * respectively in contact, thus forming a single cavity 

 provided with parietal placentas, — such a union implying 

 a more primitive or arrested condition, from an evolutionary 

 point of view ; f or they may be individually more or less 

 closed before coalescence takes place, in this case by their 

 lateral surfaces. The axile placentation is the result. The 



* The theory that the placentas are, at least in part, axial, ^Yill be 

 seen to be erroneous in consequence of the orientation of their vascular 

 cords (e.g. Fig. 12, c, p. 64; and Fig. 13, a, h, p. 65). 



t Thus the parietal placentation of Orobanche is probably a result 

 of degradation through parasitism, from the axile, of tbe ScrophularinecB. 

 It may be compared to a " cleft palate " and " hare-lip " in man. 



