70 INTERNAL GLANDS. 
elastic force of the surrounding epidermal cells, we. If anettle, 
instead of being thus touched lightly, be grasped firmly, the 
sting becomes crushed, and as it cannot then penetrate the skin, 
no irritation is produced. : 
b. Internal Glands.—These are cavities containing secretions 
situated below the epidermis, and surrounded by a compact 
layer of secreting cells (fig. 170, J, g). They are closely allied 
in their nature to receptacles of secretion (see page 72), from 
Fic. 170. Fie. 171. 
a a BB 5588 SPH TAIN IO INA 
Eee 
Qos ~ Vf Was 
0UG ay 
orn | sb y) 4 
mA r 
VSI 6 
Aso ees 
fa ESSERE 
oPSos0 
Fig.170, Internal gland from the leaf of the common Rue (Ruta graveolens). 
g. Gland surrounding a cavity, /, and itself surrounded by the epidermis, 
e,and the ordinary cells of the leaf, we.——Fig. 171. 7, 7. Internal glands 
from the rind of the Orange. 
which, in fact, in many cases, it is difficult to distinguish them, 
and amongst which, therefore, they are frequently placed. In 
some cases they are of small size, as those in the leaves of the 
Rue (fig. 170, g, 1), Myrtle, Orange, and St. John’s Wort. In 
these leaves they may be readily observed by holding them be- 
tween the eye and the light, when they appear as little trans- 
parent spots ; hence such leaves are termed dotted. This dotted 
Fie. 172. Fie. 173. Fie. 174. 
Fig. 172. Petal of a species of Ranureulus with a nectary at its base, 
covered by a scale. Fig. 173. Petal of Crown Imperial (#7itillaria im- 
perialis), with a nectariferous gland at its base. Fig. 174, Air cavities 
from the stem of Limnocharis Plumieri. 
« 
transparent appearance is due to the oily matters they con- 
tain refracting the light in a different manner to that of the 
other parts of the leaf. In other instances these glands are of 
large size (fig. 171, 7, 7), and project more or less beyond the 
surface in the form of little excrescences, as those in the 
rind of the Orange, Lemon, and Citron. Internal glands are 
