330 



liKSI.V-SECliKTING CLANDS IN SO.XtK ArSTKAI.IAX PLANTS, 



peripheral lioad-cells. Sometimes tbis tendency ]s very marked, giving- tlie gland 

 a colleter-like appearance, while often there is no sign of peripheral elongation, 

 the gland merely being a mass of polygonal cells, irregularly arranged. 



Development uf the Glands. — The first sign of gland development in On- 

 donuea viacosa, is the projection from the epidermis of a papillose cell which 

 reaches a height of about twice that of the adjacent epidermal cells (Text-tig. 

 ]«) . Tile nucleus divides and the first wall is formed in a \-ertical direction, divid- 

 ing the initial cell of the gland into two cells of equal size (Text-iig. lli). The 

 second division follows in either of the cells thus formed. The wall is either 

 placed in a slightly oblique position, when fbe resulting cells are unequal in size 

 (Text-fig. Ic) or it may be vertical, when the resulting cells are e<|ual (Text-fig. 

 1//). Whether the mature gland possesses a pedestal region, made up of two or 

 three rows of cells, depends upon the manner in which this second wall is formed 

 in the young gland. From observations on a number of glands it stems pro- 

 bable that there are never more than two vertical divisions in the first stages of 

 development, while in a number of cases there is only one. The vertical divisions 

 are followed by a series of o1)lique divisions (Text-fig. Ic-/, /(-/), which result in 

 the formation of a projecting cell mass almost spherical in contour (Text-fig. Ij). 

 At this stage there is a marked increase in the size of the cells making up the 

 gland. Those at the periphery tend to elongate in a radial manner, causing the 

 differentiation of the gland into marginal and central regions (Text-fig. Ik). 

 The mature glands are large ])eltate hairs which overlap one another and spread 

 out to cover a considerable area of the epidermis (Text-fig. 2). The multicellular 



Text-fig. 1. — (a-k). St.iges iu the develop- 

 ment of the glandular hairs of J)oJoiiaea 

 viscosa Linn, (x 200). 



Text-£ig.2. — Mature u;lands of Dodouaea 

 viscosa crowded and overlapping on 

 S'-ii-face of young loaf. Note their 

 height in comparison with thickness of 

 leaf, (x 120). 



head is borne upon a i)edestal of 2 or 3 rows of cells which- umy become more 

 numerous by later divisions. At maturity the radial elongation of the peripheral 

 cells of the gland is often partly and sometimes totally obliterated by a series of 



irregular divisions which nccur during the later stages of development (Text-fig. 



2).' 



iV. 0. LEGUMINOSExlE (Sub-order Minw.seae). 



Solereder refers to the constant formation of glandular hairs in the .Mimosene. 

 The glands may possess a uniseriate stalk of varying length, with a nuilticcllular 



