114 



MORPHOLOGY OF TISSUES'. 



furnishes on its part two layers of cells, the outer of which (d) forms a continuation 

 of the epidermis, while the inner (c) contributes to the formation of the tissue of the 

 gland, which, in its principal mass, originates by divisions of the two mother-cells of 

 the gland (/> /») ; the enveloping layer of the gland is here scarcely developed, as is 

 shown in Fig. 96 c, 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. 96 b). They always arise, as Rauter has shown, from 

 a single cell of the young epidermis which divides first vertically then tangentially 

 (Fig. 96, ^) ; thus two layers are formed, the outer of which represents a continuation 

 of the epidermis, while the inner produces, by further divisions, the tissue of the 



Fig. 96 *.— Glandular hair of Dictamnus Fraxinella (after 

 Rauter). A and B earlier stages of development ; C mature 

 gland, with the hair at its apex. 



Fig. 96 c— Internal gland of Dictamnus Fraxinella (after 

 Rauter). A and B early stages of development, C mature 

 gland; a? the covering layer, developed as a continuation of the 

 epidermis ; c and p mother-cells of the gland-tissue ; o a large 

 drop of ethereal oil. 



gland {B) ; in the further course of development, the whole substance of the gland now 

 becomes, as it were, forced outwards above the surface of the organ (C) ; and when, 

 finally, the secreting tissue is absorbed, a cavity is formed filled with mucilage and drops of 

 essential oil, and now surrounded only by the continuation of the epidermis. Whether 

 the substance of the gland is to be considered as a portion of the hair which it bears 

 must remain undecided ; it is also doubtful whether the gland should be termed an 

 internal or an external one. Similar to glands in their origin are the gum-passages and 

 gummy swellings of diseased stone-fruit. GregorieflF found the seat of the formation of 

 the gum in them to be principally the soft bast of the fibro-vascular bundles which per- 

 meate the fruit-pulp ; the cell-walls become absorbed after they have swelled up, indefi- 

 nitely bounded cavities filled with gum are thus formed, which sometimes exude their con- 

 tents externally through the flesh of the fruit when the production of gum is excessive. 

 Under the head of Superficial Glands should perhaps be included all those which 



