THE LEAVES. 



19 



{p. caHaliculatus) ; 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 



68. 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. amiplexicaulis, 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 {stipulw, Heartsease, 

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

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

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



2 



