11.8 



ELEMENTS OP STRUCTURAL BOTANY. 



Fig. 162. 



179. Base. 



s» the direction of the apex, it is seiTate, and will he 

 coarsely or finely serrate, according to the size of the 

 teeth. Sometimes the edges of large teeth are themselves 

 finely serrated, and in that case the 

 leaf is doubly serrate (Fig. 162). If 

 the teeth point outwards, that is, 

 if the two edges of each tooth are of 

 the same length, the leaf is dentate; 

 but if the teeth, instead of being 

 sharp, are rounded, the leaf is crenate 

 (Fig. 163). The term icavy explains 

 itself. 

 There are two or three peculiar modifica- 

 tions of the bases of simple sessile leaves which, are of 

 considerable importance in distinguishing plants. Some- 

 times a pair of lobes project backwards and 

 cohere on the other side of the stem, so that the 

 stem appears to pass through the leaf. This is 

 the case in our common Bell wort, the leaves of 

 which are accordingly described as perfoliate 

 (Fig. 164). Sometimes two opposite 

 sessile leaves grow togetherat the base 

 and clasp the stem, as in the upper 

 leaves of Honeysuckle, in the Triosteum, and in 

 one of our species of Eupatorium. Such leaves 

 are said- to be connate or connate-perfoliate (Fig. 

 165). In one of our Everlastings the margin 

 of the leaf is continued on each side below the 

 point of insertion, and the lobes grow fast to the sides of 

 the stem, giving rise to what is called the decurrent form 

 (Kg- 166). 



Figs. 162 to 164. — Various forms of foliage4caves. 



Fig. 163. 



Fig: 164. 



