108 MORPHOLOGY OF LEAVES. 



212. "When leaves are opposite, the perfoliation (such as that 

 of Honeysuckles, Fig. 215) is obviously the result of a congeni- 

 tal union of the bases of the pair by their contiguous edges. 

 Leaves connate in this way by narrow bases are not rare nor 

 remarkable ; but when the two are thus coalescent into one broad 

 foliaceous body, giving this appearance of perfoliation, the term 

 connate-perfoliate is used to express it. 



213. Vertical Leaves, those with blades of the ordinary kind, 

 but presenting their edges instead of their faces 



to the earth and sky, or when erect with one 

 edge directed to the stem and the other away 

 from it, are not uncommon. They prevail in 

 the Australian Myrtaceae, &c., and occur with 

 less constancy in the Californian Manzanitas, 

 and in a great variety of herbs and shrubs. The 

 anomaly involves no exception to the rule that a 

 leaf-blade is always expanded in the horizontal 

 plane, when expanded at all ; for, except in equi- 

 tant leaves, it is the result of a twist of the petiole 

 or of the blade itself. 1 In strongly marked 

 cases, or in most of them, the organization of 

 the epidermis and superficial parenchyma and 

 the distribution of the stomata are the same on 

 both faces. 



214. Eqnitant Leaves are vertical on a different 

 plan. They are conduplicate, i. e. are folded 



217 



together lengthwise on their middle, the upper surface thus con- 

 cealed within, the outer alone presented to the air and light. 



1 Silphium laciniatum, the so-called Compass Plant, and (hardly less so) 

 S. terebinthinaceum, are good instances of the kind, most of the leaves 

 making a half-twist, the radical ones by their long petioles. In the former 

 species, the pinnately parted blade occasionally makes a farther twist, so as 

 to bring the upper part into a plane at right angles to the lower. The 

 blades place themselves in various directions as respects the cardinal points ; 

 but on the prairies the greater number affect a north and south direction of 

 their edges, a peculiarity first pointed out. in the year 1842, by General 

 B. Alvord, U. S. JL 



FIG. 216. Equitant erect leaves of Iris, with the rootstock. 



FIG. 217. A section across these leaves at the base, showing the equitant character. 



