204 



PRINCIPLES OF PLANT-TERATOLOGY. 



dorsal awn, all formed in the same way ; in all these 

 cases the dorsal surface of the stipular ligule is opposed 

 to the ventral (upper) surface of the leaf, in violation 

 of the law ; this, however, may be accounted for by 

 the fact that the ligule in these cases is a mere mem- 

 branous structure, so unlike the rest of the leaf in 

 consistence and so disproportionately developed that 

 it can exert no influence in determining the facial 

 orientation of the leaf with regard to itself. 



One of the most puzzling phenomena amongst leaf- 

 abnormalities is afforded by the enations, in the form 

 of laminar or wing-like outgrowths, with reverse 

 orientation of their parts, which occur on either side 

 of the midrib of the upper or lower surface (usually 

 the latter) of various foliar organs. Only recently has, 

 what appears to be, the real meaning of it transpired. 



The foliar outgrowths described above, whether in 

 the form of laminar enations, some cases of pitcher- 

 formation, or entire leaves, really represent an attempt 

 on the part of the organ forming them to reproduce 

 itself, an attempt which is in varying degrees success- 

 ful. The three main classes mentioned in which they 

 appear all represent essentially one and the same 

 phenomenon under various disguises, viz., that of facial 

 fission of the foliar organ concerned. The type of 

 fission which takes place at right angles to this, viz., 

 marginal fission or forking, we are abundantly familiar 

 with, and it is the most usual method adopted when 

 the leaf proceeds a part, or the whole of the way, 

 towards its reproduction.* In the ferns, apparently, 

 never more than a part of this object is ever attained, 

 for the frond is never completely divided into two, the 

 organ being content with increasing its leaf-surface by 

 simple forking and cresting (cf. forked and fasciated 

 shoots, which represent the same phenomenon). 



Now, attention may be directed to the various stages 

 which are to be observed in the process of reprodnc- 



* C. de Candolle calls these two types "lateral" and " anteroposterior 

 bifurcation " respectively. 



