THEIR FORMS AND FUNCTIONS. 531 
stipules. These sheaths are connate for a short distance at the 
base only. In all these cases the young leaves, axis and in- 
florescence, are well protected by the sheaths and stipules. The 
latter serve to cover the terminal opening of the sheath the more 
effectually, and thus prevent rain from getting inside the 
sheaths. 
LIniaces. 
In Smilax the leaf-stalk is more or less winged at the base to 
protect the young bud from drying or other injury. In some 
species, e. g. S. ovalifolia, Rottb., and others, these sheaths attain 
an extraordinary size, and are turned up at the edges, forming 
pockets in which, as Burck in his paper already referred to points 
out, ants come to live. Burck thinks the large development of 
the sheath is not due to the necessity of bud-protection, but 
results from the benefit accruing to the plant from the presence 
of the ants. 
PALME. 
In Korthalsia the base of the petiole is developed into a large 
swollen ocrea: ants use the chamber thus formed as a home. 
NAIADACER. 
In Potamogeton lucens, Linn., the stipules are very long, intra- 
petiolar, and completely folded round the axis to which the base is 
adnate, and slightly overlapping along their posterior edges where 
they are entirely free, while they are entirely connate by their 
anterior edges in front of the petiole, membranous but tough, 
and 4°3-5°5 cm. long, the basal and the terminal ones being the 
shortest, but still highly developed. The only evidence of there 
being two connate stipules is supplied by the two stronger nerves, 
one cn each side of the middle line and in the position of the 
middle line in front of the petiole. Each stipular piece protects 
all the younger leaves in succession, but not their own leaf. The 
terminal bud is thus well protected by the long stipules, which 
attain a length of 4-4°3 cm. before the oldest enclosed leaf is 
liberated. The unrolling of the two sides of the lamina takes 
place from the apex downwards as the leaf gets liberated. 
Axillary buds are protected by the full-grown stipules before 
the latter become disarticulated from the stem. The first two 
leaves of axillary buds are sometimes, if not always, reduced to 
LINN, JOURN.—BOTANY, VOL. XXX. 2P 
