1 34 ORGANOGRAPHY. 



Pepper {Polygonum Hydropiper) {fig. 254), and of the Trailing 

 Fig. 254. Fig. 255. 



Fig. 2o.'>. Leaf and portion of a branch 

 oi' Salix aurita. r. Branch. 6. Bud. /• 

 Lamina with tlie upper portion removed, 

 and attached by a petiole below to the 

 stem, s s. Caulinary stipules. 



Fig. 254. Leaf and piece of the stem of Pohjgoymm Hydropiper. 

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



Sallow {Salix aurita) {fig. 255), may be taken as illnstrations 

 Fia 256 of such leaves : — the former representing 



the third portion in tlie form of a sheath 

 (f/), and the latter as stipules {ss). Irt 

 many plants, one of these parts is ab- 

 sent, and in some two, so that the leaf 

 is then reduced to but one of its por- 

 tions only. The petiole, and the sheath 

 or stipules of the leaf, are those parts 

 whicli arc more generally absent. When 

 the petiole is absent, the leaf is said to 

 be sessile ; when the stipules are absent, 

 it is e.vs1ipulate. The lamina or blade 

 is that part Avhich is most commonly 

 present. Tlie leaf is called simple if 

 there is but one blade {fig. 254), or 

 couipound if this is divided into two or 

 more separate parts {fig. 256). The 

 lamina of the ]eaf is usually that part 

 also whicli is most developed, which 



,..„ „.„ ^ , , X ^ performs the more important functions 



ttg. 2.>C, — Compound leaf of ^ „ . , „ i , • i • i • t 



Kobinia, with spiny sti- of the leaf, and wlucli IS nlso m ordinary 

 pules at its base. language known under the name of leaf. 



It is the p.art therefore, which will come more particularly 

 under our notice. Before proceeding however to describe it 

 and tlic other parts of the leaf separately, it will be far better, 

 and more convenient for us to treat of the different modes in 

 which leaves are inserted and arran<red on the stem. 



