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 shoots 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 Poiamogeion, 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- 
neae, 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 i^-g. Hydrocharis), or cordate or sagittate 
(as in Sagiftaria and some Aroidese). Branching of the 
lamina is a rather rare exception among Monocotyledons; 
and then takes the form eitlier of lobes from a broad 
common base or less often of deep divisions, as in some 
Aroideae [e.g. Amorphophallus, Fig. 141, Alherurus 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 Spadiciflorse 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 Convallaria). But when a strong mid-rib 
occurs in a broad lamina, as in Miisa &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, I the hollow 
lamina, h cavity of the lamina, i' 
inner side of the lamina, x ligule. 
