624 



PHANEROGAMS, 



it, and usually bicarinate. Of this character must be considered, for instance, the 

 upper pale of the flower of Grasses, which is itself an axillary shoot of the lower 

 pale. When the phyllotaxis of successive orders of ^oots is alternate in two rows, 

 the result of this arrangement is that a whole system of shoots is bilateral, or may 

 be divided by a plane which bisects the leaves (as in Po/amogeion, Typha, &c.). 



The mode of insertion of the cataphyllary and foliage-leaves, and very 

 often that of the hypsophyllary leaves (as for instance that of the spathe which 

 is of common occurrence), is entirely or at least generally amplexicaul, and the 

 lower part of the leaf is in consequence sheathing ; and this is evidently con- 

 nected with the want of stipules, which are so frequent 

 among Dicotyledons. The cataphyllary and many of the 

 hypsophyllary leaves are usually reduced to this sheathing 

 part, which generally passes immediately into the green 

 lamina in the case of the foliage-leaves ; but in Scitami- 

 nese, Palmaceae, Aroideae, and some others, a long and 

 comparatively slender stalk developes between the sheath 

 and the lamina. When the leaf-stalk is absent, and the 

 lamina sharply marked off from the sheath, a Ligule is 

 not unfrequently present at the point where the two meet, 

 as in Grasses and Allium (Fig. 425). 



The lamina is generally entire and of a very simple 

 form, commonly long and narrow (ligulate), rarely roundish 

 and disc-shaped {e.g. Hydrocharis), or cordate or sagittate 

 (as in Sagittaria and some Aroideae). Branching of the 

 lamina is a rather rare exception among Monocotyledons; 

 and then takes the form either of lobes from a broad 

 common base or less often of deep divisions, as in some 

 Aroideae {e.g. Amorphophallus, Fig. 141, Atherurus and 

 Sauromatuni). The division of the compound and pinnate 

 leaves of Palms is not due to a branching occurring at an 

 early stage, but to a splitting which takes place on unfold- 

 ing, and is caused by the drying up of certain strips of. 

 tissue within the lamina, which is at first sharply folded up. 

 The formation of the tendrils of Smilax appears, on the 

 other hand, to depend on actual branching of the leaf-stalk. 



The Venation of the foliage-leaves differs from that of 

 most Dicotyledons, in that the weaker veins do not gener- 

 ally project on the under side of the leaf, but run through the mesophyll ; in the 

 smaller leaves there is even no projecting mid-rib. The mid-rib is, on the other 

 hand, strongly developed in the large stalked leaves of the Spadiciflorae and Scita- 

 mineae, and is permeated by a number of fibro-vascular bundles. When the leaf is 

 ligulate and its insertion broad, the fibro-vascular bundles run nearly parallel to one 

 another ; in broader leaves without a conspicuous mid-rib they describe curves from 

 the median line to the margins (as in Convallarid). But when a strong mid-rib 

 occurs in a broad lamina, as in Musa &c., the fibro-vascular bundles which run 

 through it give off laterally smaller thin bundles which run parallel to one another 



Fig. 425.— a leaf of Allium 

 Cepa divided lengthwise ; z the 

 thickened base of the sheath, 

 which persists as a bulb-scale 

 after the upper part of the leaf 

 has died down, j the membranous 

 part of the sheath, / the hollow 

 lamina, h cavity of the lamina, i' 

 inner side of the lamina, x ligule. 



