108 



MORPHOLOGY OF LKAYKS. 



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

 of I Ione\ >nrkle^ Fig. 215) is obviously the result of a congeni- 

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

 Lea\es ,-n, mate in this way by narrow bases are not rare nor 

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

 ibliareoiis body, giving this appearance of perfoliation, the term 

 connate-perfoliate is used to express it. 



2i:'>. 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 Myrtacea-. iVc.. and oecur with 

 less constancy in the California!! 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 organi/ation of 

 the epidermis and superficial parenchyma and 

 the distribution of the stomata are the same on 

 both faces. 



214. Equitnnt Leaves are vertical on a different 

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



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

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



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

 S. lerchinthinaocnm, arc 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 pimiatelv parted blade occasionally makes a farther twist, so as 

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

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

 Init on the prairies the greater number affect a north ami south direction of 

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

 B. Alvord, I'. S. A. 



Fir.. 21fi. Kqnitant rivet lr:iv.'s of Iris, with the rootstock. 



FIG. L'17. A section across lliese leaves at tin- luisc. showing the <'</nit,int character. 



