LEAVES 7 
turf as opposed to one that is tufty. The subterranean stolons of 
some species, ¢.g. grasses of the seashore, and Agropyrum repens, 
the couch of hedgebanks and arable lands, attain a very great 
length and branch extensively underground, sending up leafy 
shoots at intervals of a few nodes, and ultimately a terminal shoot. 
Stoloniferous root-stocks are invariably perennial. The great 
abundance of grasses is largely due to their well-developed root- 
system, which enables them to supplant their rivals in the struggle 
for existence. i 
The leaves are solitary at each node and alternate; they have 
a long cylindric sheath, which is split down the side opposite the 
blade, and may be regarded as a very much compressed and in- 
volute petiole. This split sheath is one of the characters by which 
grasses are distinguished from the nearly allied family of sedges 
with entire leaf-sheaths. The sheaths closely invest the stem and 
give it a great amount of support ; at the same time they function- 
ate as leaves. At the mouth of the sheath, ze. its junction with 
the blade, there is a translucent tongue- 
like projection close pressed to the stem; 
this is known as the ligule (fig. 3). 
Sometimes the leaf is auricled, the base y 
of the blade being prolonged into a | 
short tooth or spur on each side. In Ss | 
form, the leaves are usually more or SS 
less strap-shaped (linear), always simple 4 
(undivided) and entire at their margins ; ‘oe 8B 
occasionally they are bristle-like (setace- @ ‘| 
ous). They may be flat, or folded in- 
wards from the midrib (conduplicate), ; ‘ 
or both margins may be rolled inwards re en ee 
(involute), Vernation is indicated by stem and leaf-blade. 
the form of the sheaths; when these are- 
compressed the leaves are conduplicate in bud; when the young 
leaves are involute, the sheaths are round (terete). In some species 
the leaves are flat when young but become involute when fully grown. 
Some leaves taper gradually to the apex; others are suddenly 
pointed ; others again are broadest near the middle (linear-lanceo- 
late), tapering slightly to the base as well as more finely to the apex, 
these characters being constant in each species. The midrib and 
central part of the leaf are often sunk or depressed, so as to form a 
groove or channel on the upper side, and a keel below. Venation 
is always parallel, and the veins are often unequal, every alternate 
one, third, or fourth, etc., being stouter than the others, which is best 
seen by holding the leaf between the eye and the light. There 
are often longitudinal ridges or ribs on the upper surface of the 
leaf, usually one above each vein (fig. 4) ; these ribs vary consider- 
ably in different species, as regards their number and prominence, 
and may be flat, rounded or acute at the top ; sometimes they are 
only perceptible as faint striations. Both surfaces of the leaf may 
be hairy or downy; commonly the upper surface only is so. 
