THEIR STRUCTURE AND FORMS. 



107 



cies, some of which are moderately, and most of them strikingly, 

 oblique in this way. Elm-leaves, and the like, are more or less 

 inequilateral at the base. 



211. Connate and Perfoliate Leaves. These are explained by 

 the union of con- 

 tiguous leaf-edges. 

 Peltate leaves, to 

 which a paragraph 

 has already been 

 given (182), come 

 under the same 

 head ; the seeming 

 attachment of the 

 petiole to the lower 

 face of the blade 

 being the result of 

 a congenital union 

 of the edges of the 

 sinus. In a sessile 

 leaf, when such a 213 



union takes place, it surrounds and encloses that portion of the 

 stem ; which is thus perfoliate. (Fig. 

 213, 214.) It is the stem which is 

 literally perfoliate, i.e. which seem- 

 ingly passes through the leaf ; but it 

 is customary, though etymologically 

 absurd, to call this a perfoliate leaf! 

 Uvularia perfoliata (Fig. 213), in the 

 later growth of the season, reveals the 

 explanation of the perfoliation : the 

 base of the lower leaves conspicuously 

 surrounds and encloses the stem : that 

 of the upper is merely cordate and 

 clasping ; the uppermost simply ses- 

 sile by a rounded base. Baptisia 

 perfoliata (Fig. 214) is a more 

 strongly marked case of perfoliation. 

 But there are good morphological 

 reasons for inferring that this seemingly simple leaf consists of 

 a pair of stipules and a leaflet combined. An occasional mon- 

 strosity verifies this supposition. 



FIG. 213. Leafy branch of Uvularia perfoliata. 



FIG. 214. Leafy and flowering branch of Baptisia perfoliata. 



FIG. 215. Lonicera flava, a wild Honeysuckle, counate-perfoliate as to the upper 

 leaves. 



