GLANDS. 



183 



characteristic contents of the passage itself are already recognisable as such in the 

 epithelium cells. Possibly the substance of the wall of the epithelium itself becomes 

 chemically altered and concerned in the formation of the secretion. 



All receptacles for secretions not consisting of long vesicles, series of vesicles, 

 or long intercellular passages, were formerly collected together under the name of 

 Glands. We shall employ this expression quite arbitrarily for a special kind of re- 

 ceptacles for secretion, which chiefly contain ethereal oils and resins dissolved in them ; 

 and we shall at the same time distinguish two subdivisions of these structures — the 



Fig. 1S3. — Gland on the upper side of the leaf 

 oi Diclamnus Fraxi}ulla (after Ranter). A, B ■ 

 early stages of development ; C mature gland ; d 

 the covering layer forming a continuation of the 

 epidermis; c s.n& p mother-cells of the gland- 

 tissue ; c a large drop of ethereal oil. 



FIG. 184.— Gland with hair, from the inflorescence 

 o( IJictanintts Fraxitteiia (after Rauter). jt, B early 

 stages of developmeut ; r mature gland witli the hair 

 {h) at its apex. 



internal glands, i.e. those situated under the epidermis, on the one hand; and the so- 

 called epidermal glands, which belong to the epidermis and its hairs, on the other. 



The internal glands are often perceptible to the unaided eye as bright, trans- 

 lucent dots in the tissue of foliage leaves or stems, e. g. in the leaves of the Citrons 

 and Oranges, many species of Hypericum, Lysimachia, etc. ; or they are contained in 

 protuberances of the outer surface, as in Dictamnus Fraxinella. The internal glands 

 in the skin of the fruit of the Orange are very conspicuous and large ; they abound 

 in ethereal oils, and appear in transverse and longitudinal sections as roundish 

 cavities, from which the inflammable ethereal oil spurts on the application of pres- 

 sure. Such glands originate, so far as investigation extends, from a single mother- 



