32 BOTANY part i 



that are dissected and filiform in character. The pointed extremity of the foliage 

 leaves of many land plants, according to Stahl, facilitates the removal of water 

 from the leaf surface. Fleshy so-called succulent leaves, like fleshy stems, serve 

 as reservoirs for storing -water. 



In Monocotyledons the leaf-base very often forms a sheath about 

 the stem ; in Dicotyledons this happens much less frequently. In the 

 case of the Gramineae, the sheath is open on the side of the stem 

 opposite the leaf-blade (Fig. 31, v), while in the Cyperaceae it is com- 

 pletely grown together. The sheath of the grasses is prolonged at the 

 base of the lamina into a scaly outgrowth, the ligule. Such a sheath, 

 while protecting the lower part of the internodes which remain soft 

 and in a state of growth, gives them at. the same time rigidity. 



Stipules. — These are lateral appendages sometimes found at the 

 base of leaves. When present they may be either small and incon- 

 spicuous, or may attain a considerable size. When their function is 

 merely to protect the young growth in the bud, they are usually of a 

 brown or yellow colour, and are not persistent ; whereas, if destined to 

 become assimilatory organs, and to assist in providing nourishment, 

 they are green, and may assume the structure and form of the leaf-blade, 

 which sometimes becomes modified and adapted to other purposes 

 (Figs. 35, 36). Normally, the stipules are two in number, that is, one 

 on each side of the petiole. In many species of Galium, where the 

 stipules resemble leaf-blades, the leaf-whorls appear to be composed of 

 six members, but consist actually of but two leaves with their four 

 stipules, which may be easily distinguished by the absence of any buds 

 in their axils. In other species of the same genus (Galium cruciatwm 

 and palustre) there are only four members in the whorls, as each two 

 adjoining stipules become united. In many cases the stipules have the 

 form of appendages to the enlarged leaf-base. Sometimes both 

 stipules are united into a single one, which then appears to have an 

 axillary origin ; or the stipules may completely encircle the stem, and 

 thus form a sheath about the younger undeveloped leaves. This 

 sheath-like fusion of the stipules may be easily observed on the India- 

 rubber tree (Ficus elastica), now so commonly grown as a decorative 

 plant. In this case the stipular sheath is burst by the unfolding of 

 each new leaf and pushed upwards on the stem. In the Polygonaceae 

 the stipular covering is similarly torn apart by the developing leaves, 

 but then remains on the stem in the form of a membranous sheath 

 (ochrea). 



Scale Leaves possess a simpler structure than foliage leaves, 

 and are attached directly to the stem, without a leaf-stalk. They 

 exercise no assimilatory functions, and are more especially of service 

 as organs of protection. Scale leaves exercise their most important 

 function as bud-scales ; they are then hard and thick, and usually 

 of a brown colour. They most frequently take their origin from 

 the enlarged leaf-base ; in that case the upper leaf either does not 



