512 



SECRETORY AND EXCRETORY SYSTEMS 



large number of cells, as in Sanguisorba carnea. The stalk-cells some- 

 times contain chlorophyll, in which case they represent a localised 

 photosynthetic apparatus, belonging to the gland. Glandular villi (or 

 glandular shag-hairs, " Driismzotten ") like ordinary glandular hairs 



Fio. 207. 



Dermal Glands. A. Ordinary glandular hairs from a petiole of Pelargonium zonule ; 

 2, secretory cell ; s, secretion. B. Young () and adult (b) glandular scales from a leaf 

 of Ribes nigrum (the secretion removed by treatment with alcohol) ; z, secretory cells ; 

 v, glandular cavity formed by distension of the cuticle. 



are usually differentiated into a stalk, which here consists of an elon- 

 gated mass of cells, and a secretory head, which is generally multi- 

 cellular ; not infrequently, individual cells of the massive stalk are 

 produced into simple glandular hairs (e.g. Begonia Rex). Glandular 

 scales, finally, likewise possess more or less well-developed stalks, but are 



characterised, as their name indicates, by the fact 

 that the secreting elements are arranged in the 

 form of a flattened scale, or, in some cases, of an 

 almost basin-shaped cell-plate. As examples of 

 glandular scale we may mention the well-known 

 lupulin-glands of the Hop, and the glandular scales 

 which occur in Ribes nigrum, and in species of 

 Tli I/ mvs, Mentha and Satureja. In Pyrethrum Bal- 

 sa mi fa (Fig. 208), each glandular hair consists of 

 a cell-plate, extended at right angles to the 

 surface of the parent organ and made up of four tiers of two cells 

 each. The cells of the uppermost tier are colourless and represent the 

 actual secretory organs ; those of the two next tiers contain numerous 



Fig. 20S. 



Glandular scale of Py- 

 rethrum Balsam it n . 



