128 



ORGANOGRAPHY. 



Fig. 247. 



Fig. 248. 



Fig. 248. Leaf and portion of a branch 

 ot Salix aurita. r. Branch. &. Bud. /. 

 Lamina with the upper portion re- 

 moved, and attached by a petiole, p, 

 to the stem, s, s. Caullnary stipules. 



Fig. 247. Leaf and piece of the stem of Polygonum ffydropiper. 

 I. Lamina or blade, p. Petiole, d. Sheath or vagina. 



limb ; of a narrower portion, by which the lamina is connected 

 with the stem, called the petiole or leaf -stalk (p) ; and of a por- 

 tion at the base of the petiole, or of the lamina if the petiole is 

 absent, which either exists in the form of a sheath or vagina (d) 

 encircling the stem, or as two little leaf-like appendages on each 

 side, which are called stipules (Jig. 248, ss). 



Fiq. 249. These three portions are by no means 



always present, though such is fre- 

 quently the case. Thus, the leaves of 

 the Water Pepper {Polygonum Hydro- 

 piper) {fig. 247), and of the Trailing 

 Sallow {Salix aurita) {fig. 2^%), may be 

 taken as illustrations of the most highly 

 developed leaves, namely, — those in 

 which all the parts are found ; but 

 in many plants one of these parts is 

 absent, and in some two, so that the 

 leaf is then reduced to but one of its 

 portions only. The petiole, and the 

 sheath or stipules of the leaf, are those 

 parts which are more generally absent. 

 When the petiole is absent, the leaf is 

 said to be sessile {fig, 260) ; when the 

 stipules are absent, it is exstipulate. 

 The lamina or blade is that part which 

 Fig. 249.-Compound leaf of js most commonly present. _ The leaf 

 Robinia, with spiny stipules is called simple if there is but one 

 ^' ^^' ''^^^- blade {fig. 247), or compound if this is 



divided into two or more separate parts ( fig. 249.) The lamina 



