MORPHOLOGY OF THE VEGETATIVE ORGANS 105 
The uppermost sheath of Sporobolus cryptandrus (Torr.) Gray 
and allied species becomes inflated and spathe-like, more or less 
inclosing the inflorescence. The spathe-like sheaths are conspicuous 
in Andropogon Elliottii Chapm. Certain water-grasses, notably Pas- 
palum repens Berg., have inflated sheaths that act as floats to sus- 
tain the stems on the surface of the water. In some grasses, especi- 
ally those of dry regions, the dead sheaths persist as separated fibers 
or as a network of fibers. In other species such as Muhlenbergia 
gracilis (H. B. K.) Kunth and more conspicuously in M. straminea 
Hitche., the sheaths become flat and ribbon-like and persist as a 
curly mass resembling shavings, simulating old blades. 
In some species the sheaths are united by the margins 
to form a tube nearly or quite to the top. 
Examples: Bromus, Danthonia, Festuca, Melica, Panicularia. 
Though the sheaths normally encircle the culm, a 
spreading branch may pull the subtending sheath away 
from the culm, in which case the sheath usually encircles 
the branch. 
133. Sheath nodes—Many grasses present at the 
base of the sheath a distinct swelling which at first sight 
appears to be the node of the culm. If this portion of the 
stem is split open longitudinally it is readily seen that 
the prominent swelling is on the sheath and that the stem 
node is just below as will be indicated by the cross parti- 
tion. The sheath-node is often differentiated also by its 
color or pubescence. 
134. The collar— At the junction of the sheath and 
blade there is in nearly all grasses a distinct line of demar- 
kation. On the inside is the ligule (Par. 135). On the out- 
side or back is a line, zone or ridge which is differentiated 
in color, texture, markings or pubescence. This zone is 
called the collar. 
135. The ligule is an appendage on the inside of a 
