30 



stem, the petiole may, or may not, be terete, flattened, 

 angled, grooved, striate, and so on. Very frequently it is 

 channelled, or grooved, on the upper surface as in Viburnum 

 cotinifolium, see Figs. 8 and 9, Plate IX. 



In some cases the lamina is continued along the sides of 

 the petiole which thus appears to be winged, as seen in the 

 Orange. 



Leaf-Base. 28. In some cases [the base of 



the leaf is more or less clearly differentiated from the rest 

 of the leaf and in many plants it becomes a swollen cushion of 

 tissue called the pulvinus, well seen for example at the base 

 of the petiole of Millettia auriculata, and the small pulvinus 

 often found at the base of leaflets is called a pulvinule. 



. This differentiation, however, is particularly remarkable in 

 many Bamboos in which the leaf-base is large and forms a 

 long sheath to the stem, the petiole of the lamina being 

 separated from the sheath by a distinct joint or articulation. 

 The sheaths which arise directly from the Bamboo culms, 

 called the culm -sheaths, in the axils of which the branches 

 arise, usually develop no leaf -blade, or only an imperfect one, 

 but all gradations between sheaths with no blade and those 

 with a normal lamina may frequently be seen. 



This sheath is very characteristic of Bamboos and Grasses 

 generally, as is also the peculiar structure known as the ligule, 

 a membranous outgrowth developed from the inner face of 

 the leaf -sheath at the junction of the lamina, or petiole, with 

 the leaf-sheath, and which may be well seen in Arundinaria 

 falcata. 



In Berberis Lycium a distinct joint is found between the 

 leaf-base and the lamina of the apparently simple leaf, see Fig. 

 4, Plate V. In Berberis nepalensis, however, a plant which 

 in important characters resembles B. Lycium and which there- 

 fore, being considered to be fairly closely related to it, bears 

 the name of Berberis, the leaves are pinnate and there is a 

 distinct joint between the terminal leaflet and the rest of 

 the leaf and at the insertion of the lateral leaflets, see 

 Fig. 3, Plate V ; hence it is concluded that the leaf of B. 

 Lycium is really a compound, i.e. pinnate, leaf, reduced to 

 the terminal leaflet. The apparently simple leaf of the 

 Orange is also articulated to the petiole and is considered to be 

 a unifoliolate compound leaf. 



Stipules. 29. The leaf -base frequently de- 



velops two more or less noticeable lateral branches called 



