THE EPIDERMAL TISSUE. 



lOI 



Glandular Hairs. These consist of a stalk and a terminal head which is either com- 

 posed of a single cell filled with resin or a volatile oil, or constitutes a true Gland, 

 made up of a number of cells which have coalesced, so that nothing remains but the 

 external cuticularised cell-wall in the form of a hollow vesicle containing the secretion. 

 The oily, viscid, odoriferous secretion not unfrequently penetrates through the cell-wall, 

 and raises the cuticle in the form of a bladder, collecting beneath it as a clear fluid, 

 while the cells which produce it partially or entirely disappear, as in Salvia, Cannabis, 

 and Humulus, in the latter case on the perianth of the female flowers. We are indebted 

 to a careful work by Hanstein ^ for an accurate knowledge of the glandular hairs 

 on the leaf-buds of many trees, shrubs, and herbs. The parts of the bud are coated 

 by a gummy substance, or one composed of gum- mucilage and drops of balsam, which 

 he calls Blastocolla, while the glandular hairs which produce them he terms Colleters. 



Fig. 83. — Development of the hairs on the calyx of a flower-bud of the hollyhock (X 300) ; A luk woolly hairs on the 

 inner surface; b and c glandular hairs in different stages of development; at a in ^ rudiment of a glandular hair; 

 ep always signifies the (still young) epidermis. The figures a.\r\. A,^ in C, and 7 in /? show the first stages of develop- 

 ment of the stellate hairs (or rather tufts of hairs), the subsequent condition of which may be compared in Fig. 42 (p. 43) ; 

 at ^ « is the hair in longitudinal section; /3 and 7 show the appearance seen from above ; the cells are rich in proto- 

 plasm ; the formation of vacuoles (t/) in the protoplasm is beginning in y. 



These shortly-stalked multicellular hairs springing from an epidermal cell may expand 

 towards the apex in a strap-shaped manner (Rumex), or may bear cells arranged in 

 a fan-like manner on a kind of mid-rib {Cunonia, Coffea), or may form spherical or club- 

 shaped knobs {Ribes sanguineum, Syringa 'vulgaris) ; in Platanus acerifoUa branched rows 

 of cells occur, the roundish terminal cells of which are glandular. The colleters attain 

 their full development at a very early period in the bud, when the foliar structures 

 and portion of the stem out of which they spring are still very young and consist 

 of tissue which is scarcely diff"erentiated. They are borne especially on the en- 



^ Ueber die Organe der Harz- nnd Schleimabsonderung in den Laubknospen, Bot. Zeitg. iS68, no. 

 43 et seq. The very instructive illustrations to this paper should be consulted.— See also Martinet, /. c. 



