242 SIR JOHN LUBBOCK ON STIPULES, 
PLATANACER. 
The case of Platanus is very interesting. The winter-buds 
are covered by a number of cap-like stipules, the leaves belong- 
ing to which have become completely aborted. The outer 
stipule or cup is brown or reddish brown and secretes a gummy 
substance on its inner surface, besmearing the bud as in the 
Horse-chestnut, but only in the very early stages. As the bud 
swells the outer cap becomes ruptured and appears then like a 
deeply concave scale, which is glabrous or nearly so. This is 
followed by others which attain a larger size before the ex- 
panding bud causes them to split; they are densely covered 
with brown hairs externally and glabrous internally. 
Drrsacez. 
In the Teasel (Dipsacus) the bases of the petioles are expanded 
and connate, thus forming a large cup, which generally contains 
water. It has been suggested by Kerner that this water forms 
a sort of moat which protects the flowers from ants and other 
creeping insects. On the other hand, Mr. Francis Darwin thinks 
that insects &c. are drowned in the water, and thus supply the 
plant with animal food. He has described certain curious 
protoplasmic threads, emitted by some of the cells, which he 
suggests may serve to absorb the nourishment thus supplied. 
URTICACER. 
In the Hop (Humulus Lupulus) the stipules are intrapetiolar, 
connate for å or 4 of their length; each pair forming an ovate 
10-nerved piece, with the tips ovate and free. These sheaths 
effectively surround and protect the growing axis. This type 
occurs in other species of climbing plants. 
CONCLUSION. 
On the whole, then, where we find in the same family or genus 
some species with, and some without, stipules, I believe that as 
a general rule this difference has reference to the mode of pro- 
tection of the bud. This important function is effected in 
various ways,—by tle stipules, by the base of the leaves, by the 
more or less expanded base of the petiole, by the pedestal of the 
petiole, by scales, by hairs, by gummy secretions, &c. 
The protection of the bud seems then to be the most general 
reason for the presence of stipules, though sometimes they take 
