THE LEAVES. 



19 



(p. canaliculatus) ; flattened horizontally, or depressed (p. depressus)', flattened 

 laterally or compressed (p. compressus) ; in this case it is usually flexible, and the 

 pendulous blade trembles with every breath of wind (Aspen). 



The petiole is usually of tolerably uniform diameter throughout its length 

 (p. continuus, Ivy, fig. 47) ; but it may be much dilated in the middle, and thus 

 resemble a blade separated from the true blade by a constriction, when it is winged 

 (p. alatus, Orange, fig. 55, P; Acacia heterophylla, fig. 56). Lastly, a dilated petiole 



58. Wheat. Sheathing leaf. 



69. Clematis. Twining petiole. 



may replace the true blade, when it is called a phyllode (phyllodium), as in most 

 Australian Acacias. When the enlarged base of the petiole, and the node from which 

 it issues, occupy a large portion of the circumference of the stem, the petiole is 

 called amplexicaul (p. amplexicaulis, Ranunculus, fig. 57) ; if the entire petiole is 

 enlarged, and sheathes the stem, the leaf is called sheathing (vaginans, Carex, Wheat, 

 fig. 58). 



The direction of the petiole is usually straight, but in some plants it twines 

 round neighbouring objects (Clematis, fig. 59). 



Stipules. A leaf is stipulate (/. stipulatum), when provided at its base with 

 appendages more or less analogous to leaves, named stipules (stipula?, Heartsease, 

 fig. 60). These may be persistent (s. persistentes), when they persist as long as 

 the leaf which they accompany (Heartsease, fig. 60) ; or caducous (s. caducce), when 

 they fall before the leaf, or as soon as the shoot lengthens (Willow, Oak). 



c 2 



