92 
MORPHOLOGY OF TISSUES. 
filled with watery protoplasm with large drops of a volatile oil floating in it. The 
layers of cells which surround the cavity form an envelope, which differentiates it 
sharply from the surrounding tissue. The origin of two different forms of gland 
in Dictamnus Frax'inella is illustrated in the accompanying figures, taken from Rauter ^. 
Fig. 76 represents the development of a gland on the upper side of the leaf, the contents 
of which are the source of the powerful odour of the plant. These leaf-glands of 
Dictamnus originate from only two cells, one of which belongs to the young epidermis, 
the other to the subjacent parenchymatous layer; the former divides again into two 
layers of cells, the outer of which {d) forms a continuation of the epidermis, while 
the inner one {/) contributes to the formation of the tissue of the gland, the principal 
Fig. 76.— Gland from the upper side of the leaf oi Dictam- 
nus Fraxmella (after Rauter). A and B early stages of de- 
velopment, C mature gland; d the covering layer, forming 
a continuation of the epidermis ; c and p mother-cells of the 
gland-tissue ; 0 a large drop of volatile oil. 
Fig. 77. — Gland and hair from the inflorescence of 
Dicta7n7ius Fraxi7iena (after Rauter). A and B early 
stages of development ; C mature gland, with the hair h 
at its apex. 
part of which originates by divisions of the two mother-cells of the gland {p p) ; the 
enveloping layer of the gland is here but slightly developed, as is shown in Fig. 76, C. 
On the flower-stalks, bracts, and sepals of the same plant are formed large sessile or 
shortly-stalked glands of somewhat ovoid form, bearing at their apex a single hair 
(Fig. 77, h). These always arise, as Rauter has shown, from a single cell of the young 
epidermis, which divides first vertically, then tangentiafly (Fig. 77, ^) ; thus two layers 
are formed, the outer of which is a continuation of the epidermis, while the inner 
produces, by further divisions, the tissue of the gland {B). In the further course of 
^ Rauter, Zur Entwickelungsgescliichte einiger Trichomgebilde. Wien 1871. 
