

~ NATURAL ORDERS "148 
GRAMINEZ. 
tori Grasses are easily recognised and distinguished 
Characters. from all other plants by certain external characters. 
1. The stem, if cut across, is usually circular in outline ; it 
is also hollow, except at the nodes. At the node a swelling 
may be seen; this is a pulvinus. If grass is trampled on or 
beaten down by rain it becomes “laid”; then the lower side | 
of the pulvinus elongates, and brings all the part of the grass 
above it into an erect position. : 
2. The leaves are arranged in two rows alternately. Hach 
leat consists of a blade, which passes directly without a leaf- 
stalk into a sheath. At the junction of the blade with the 
sheath there is an outgrowth of the blade called the ligule ; 
its function is probably to prevent the water which has run 
down the leaf getting into the sheath and rotting the stem. 
The sheath is nearly always split, and the leaves are usually 
elongated in form (Plate IX., Fig. 136). 
3. The roots of Grasses are usually fibrous, arising from the - 
nodes. Grasses may be annuals, biennials, or perennials. If 
all the shoots have flowering stems of this year’s growth, then 
the Grass is an annual ; if it has leaves only, it may be an_ 
annual or perennial; the latter will probably have more leaf- 
scars than the former. 
The only plants with which Grasses could possibly be con- 
fused are Sedges and Rushes. The former have solid angular 
- stems, with leaves in three rows; the latter are generally 
readily distinguished by their cylindrical leaves, and always | 
by the membranous perianth of the flowers. 
The inflorescence of a Grass consists of a principal stalk, 
called a ‘“‘haulm” or “culm,” on which shorter stalks are 
arranged, ach short stalk bears a spikelet, consisting of 
scale-like structures, in the angles of which are situated the 
_ flowers. The inflorescence of a Grass, such as Wheat or Oat, 
consists of several spikelets placed more or less closely one 
above the other. If a spikelet is removed and examined it 
will be seen to consist of the following structures: On the 
