376 



BOTANY 



(Hyplicene Thebaica), of Upper Egypt, and perhaps Pandanus, but 

 this has not been critically investigated. 



The Leaf 



The leaves of Monocotyledons are usually simple in form, the 

 commonest type being the lanceolate or linear, sessile leaf, with 

 entire margin. The leaf may have a definite midrib, but often the 

 parallel veins are all alike. A petiole is sometimes present, as in 

 the Palms and Araceae; and in these the leaves may be of great 

 size. True compound leaves occur in some Aracese (e.g. Ariscema 



FIG. 347. A, Agave America. ia, cross-section of leaf (X 4) ; h, colorless hypo- 

 derma; p, palisade-parenchyma; vb, vascular bundles. B, Erythronium Ameri- 

 canum, epidermal cells and stomata (X75). C, Tradescantia zebrina, stoma 

 with four accessory cells (x 200). D, Iris xiphium, cross-section of stem (x 4) ; 

 vb, vascular bundles. E, stoma of Zea Mays ; x, accessory cell ; g, guard cell 

 (X600). 



triphyllum), but the apparently compound leaves of Palms owe their 

 pinnate form to a tearing into strips of the originally entire lamina. 

 The attachment of the leaf -base may be narrow, but it is common 

 to find it- much expanded, and often developed into a large sheath, 

 which envelops the internodes of the stem. Such sheaths are 

 especially conspicuous in the Grasses and Sedges (Fig. 358, C), and 

 in many aquatic forms, like the Pondweeds and in the Palms. 

 Free stipules are never found. In most aquatic Monocotyledons, 

 between the sheaths are found membranous axillary scales, which 

 sometimes resemble stipules. Sometimes paired outgrowths (ligules) 

 are formed at the junction of the sheath and the base of the lamina 

 (Fig. 358, C). 



