THE NATURAL HISTORY OF BRITISH GRASSES. 25 
is sometimes large and drooping, as in the larger or flag- 
like grasses, but occasionally it is very minute, especially 
when compared with the sheath, as in the Avena pubescens 
(soft oat-grass). In some species the blade is long and the 
sheath short. The blade is traversed by longitudinal paral- 
lel lines, which are called the leaf-veins or nervures : these 
may be broad, narrow, rigid, soft, armed with rough hairs, 
and so on, all of which are not only points of distinction in 
species, but aid in making up the sum of those differences 
which will ever be found in good and bad pasture grasses : 
as, for instance, grasses in which the herbage is covered 
with long downy hairs are mostly poor and innutritious in 
quality; on the other hand those of a harsh and rigid 
structure, with serrated leaves, whose edges act as a saw 
and whose flat blades perform the office of a file, even if 
nutritious, would nevertheless be refused by cattle on ac- 
count of their mechanical inconvenience. 
The ligule—At the point where the sheath ends and 
the blade begins occurs a thin and usually white semi- 
transparent membrane, termed the ligule, or tongue. 
This, as it varies so much in size and form, will be fre- 
quently referred to in diagnosis by some such terms as the 
following :— 
Short, in Poa pratensis, smooth-stalked meadow-grass. 
Pointed, in Poa trivialis, rough-stalked ditto. 
Notched, in Bromus mollis, soft brome or lop grass. 
In pairs, in Ammophila arundinacea, common sea-reed. 
Its value as a distinctive character may be drawn from 
an examination of Poa pratensis and P. trivialis, as it assists 
at a glance to distinguish two grasses, much alike in appear- 
ance, though very distinct in habit and general properties. 
The use which this part of the leaf subserves would ap- 
pear to be that of more securely fastening the upper part 
of the sheath to the culm, as without it the wind would tear 
the leaves downwards, in which case their functions would 
become much disturbed, and they would soon wither and 
die. The flower in grasses consists of the elements of an 
