FOLIAGE-LEAVES 



IS 



■expanded and flattened basal sheath, by which the leaf is 

 attached to the stem. The sheath frequently bears two lateral 

 outgrowths known as the stipules {nb). 



(i.) THE SHEATH. 



The sheath of a leaf may be well developed {e.g. Butter- 

 cup, Carrot, Cowparsnip), but frequently it is not distin- 

 guishable. 



The stipules (fig. 17 nb) usually take the form of two 

 flattened expansions of the leaf-sheath. They are parts of a 

 single leaf A leaf possessing stipules is 

 described as stipulate ; a leaf devoid of 

 stipules is said to be exstipulate. Most 

 frequently the stipules are small, and 

 serve merely to protect the young grow- 

 ing leaves of a bud : in which case they 

 drop off {e.g. Pear) or shrivel as they 

 unfold from the bud. But the stipules 

 may form good-sized green plates, which 

 persist as long as the leaf -blade — 

 e.g. Hawthorn (fig. 58 n), Pea (fig. 59 n), 

 Violet. In the rhubarb-family, the two 

 stipules of each leaf are replaced by a 

 membranous pipe embracing that part 

 of the stem which is near the leaf 



The leaf of a grass has a long tubular 

 sheath which surrounds the stem, but 

 is usually split down; one side. The leaf 

 possesses no stalk, so that the sheath is 

 directly continuous with the blade. At the junction of the 

 blade and sheath a. small membranous plate — the ligule — 

 stands out from the upper face of the leaf. 



-sp 



Fig. 17. — Leaf of Pear. ■ 

 . (After Dennert.) 



(ii.) STALK OR PETIOLE. 



The stalk varies in length : in fact, it may be entirely absent, 

 in which case the leaf is said to be sessile. Generally the 

 stalk is attached to one end of the blade ; rarely it is fixed 

 to the lower face of the lamina, as in the garden Tropceolum 

 (commonly, though incorrectly termed " Nasturtium "). 



