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 difVcrentiates it 

 sharply from the surrounding tissue. The origin of two different forms of gland 

 in Dictamnus Fraxinella 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 (r) 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 Fraxinella (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 ; o a large drop of volatile oil. 



Fig. 77.— Gland and hair from the inflorescence of 

 Dictamnus Fraxinella (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 tangentially (Fig. 77, A)\ 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 (J5). In the further course of 



' Rauter, Zur Entwickelungsgescliichte einiger Trichomgebilde. Wien 187 1. 



