E. R. Saunders 155 



(hydathode). The vascular elements end in a mass of closely packed 

 cells devoid of chlorophyll and with conspicuous nuclei. In most leaves 

 this terminal gland is the only one present. Exceptionally, where one 

 or two strong lateral veins occur, they also terminate in a hydathode 

 giving rise to a well-marked lateral tooth. In the epidermis covering 

 the glands, as elsewhere, stomata of varying size and in all stages of 

 development are abundant. The intervening cells here and over the 

 whole leaf surface vary considerably in size. Those which grow out 

 into hairs show a bulbous basal region and an upper free portion 

 characteristically branched. The walls are cuticularised and very much 

 thickened. The thickening takes place not only in the whole extent of 

 the exposed wall but in the lower sunk portion as well. It may even 

 involve the outer wall of neighbouring cells though these cells do not 

 themselves grow out into hairs. In a surface view of the epidermis the 

 somewhat small bulbous base forms a centre round which the larger 

 neighbouring cells become arranged, more regularly than elsewhere, as 

 a rosette. It is somewhat interesting that although stomata are ap- 

 parently formed continuously as required, the hairs all develop when 

 the leaf first makes its appearance. Whatever the causes which lead 

 to hair formation they are evidently operative only at the moment when 

 the leaf originates, unless it be that none of the rest of the epidermal 

 cells possess the capacity to produce hairs, or that at a later stage 

 hair formation becomes physiologically impossible. 



I. Hoary. (PL Vlt, figs. 1—4.) 



1. Fully hoary. M. incana type, as scarcely needs to be recalled, 

 has all green parts above the cotyledonary leveP, i.e. stem, leaf, axis 

 of the inflorescence, pedicel, calyx and ovary thickly covered with a 

 tomentum which gives the plant a grey appearance (PI. VII, fig. 1, left- 

 hand pod). As the pod elongates after fertilisation the stigma lobes 

 enlarge to form two pincer-like knobs or horns, which are likewise 

 clothed with hairs though less thickly than the rest of the pod. All 

 four petals in the single and several outer ones in the double^ sometimes 

 show a sprinkling of hairs in patches here and there on the outer surface 

 (PL VII, figs. 2, 3, 4), but quite often they are completely glabrous. Hair 



^ The cotyledons and hypocotyl of every grade including incana are absolutely glabrous. 



^ In the earlier account (Journal of Geneticx, Vol. v. No. 3, p. 146) it is stated that 

 these coroUine hairs are confined to the doubles, none having at that time been seen on the 

 singles. It now appears that they are about as frequent and erratic in their distribution 

 in the one case as in the other, and we cannot therefore base any argument as to the more 

 primitive nature of the double on this ground. 



