312 ON NAIAS GRAMINEA DEL., VAR. DELILEI MAGNUS. 
VIL.-—Tue Lear-sHEata. 
The leaf-sheath is another impor sn distiio mene 
: , portant character in distinguishin 
a species of Naiade, the extent of the dilatation, and ‘he fe at 
6 ue when present, furnishing useful marks of discrimination. 
e€ 
Fie. 53. 
types given by 
Braun in the ‘Journal 
tenuifolia. 
In the English Natas 
graminea the base of the 
mina of the outermost 
or less ample sheath (see 
fig. 52); the size of the 
sheath presents con- 
cording to the age and 
the position of the leaf 
to which it belongs (see 
figs. 52 to 55). Isee no 
such as are foun 
Naias major and in theal- 
in situ ; one of the scales 
is drawn separately m 
fig. 80 on the same 
plate. 
The auricles in their 
turn v i and 
size, but I have not met 
