50 
ORGANOGRAPHY. 
BOOK I. 
tremities, and are often confounded with the glandular hairs 
above described, from which they have been well distinguished 
by Link. According to that botanist, they are either simple 
or compound ; the former consisting of a single cell, and 
placed upon a hair acting as a simple conduit, occasionally in- 
terrupted by divisions ; the latter consisting of several cells, 
and seated upon a stalk containing several conduits, formed 
by rows of cellular tissue. They are common upon the rose 
and the bramble, in which they become very rigid, and as- 
sume the nature of aculei. For the sake of distinguishing 
them from the latter, they have been called setcB by Woods 
and myself, but improperly ; they are also the aiguillons of the 
French. In Hypericum they abound on the calyx and corolla 
of some species, but do not give out any exudation ; they con- 
tain, however, a deep red juice within their cells. In some 
Jatrophas they are much branched ; in many Diosmeae they 
form a curious humid appendage at the apex of the stamens. 
Sessile glands, verrucce^ or warts, are produced upon various 
parts, and are extremely variable in figure. In Cassias, they 
are seated upon the upper edge of the petiole, and are usually 
cylindrical or conical ; in Cruciferous plants they are little 
roundish shining bodies, arising from just below the base of 
the ovary ; in the leafless Acacias they are depressed, with a 
thickened rim, and placed on the upper edge of the phyllo- 
dium ; they are little kidney-shaped bodies upon the petiole 
of the Peach and other drupaceous plants ; and they assume 
many more appearances. They are common upon the petiole, 
as in Passiflora ; they are also found upon the calyx, as in some 
species of Campanula, and at the serratures of the leaves, 
when they are considered by Roper (De Florihus Balsaminea- 
rum, p. 15.) to be abortive ovules ; and they appear upon the 
pericarp and the skin of the seed ; in the latter case they are 
called spongiolce seminales by De Candolle. They are remark- 
able in Dionaea muscipula for growing from the mouth of the 
stomates ; and in Nepenthes for closing up the same organs by 
forming underneath them. (See page 42.) In the latter 
plant they are found, moreover, in the form of hard brown 
concretions, lying beneath the cuticle, at the bottom of the 
pitchers. In figure they are round, oblong, or reniform, and 
