A. H. Trow 275 



NOTES ON THE ILLUSTRATIONS (Plates XV XVIII). 



All the photographs were prepared from the crops of 1912, which includeil colonies of 

 all the types refeiTed to in the paper. Certain new features of interest were observed for 

 the tirst time in lyl2, such as the unexpected appearance of the single specimen of a 

 cream coloured, Jiiiihriale, multicaulis represented in Fig. "20, PI. XVII. These are reserved 

 for furtlier consideration and a later rejiort. Two points, dealing with the ray character 

 and hairiness, deserve a brief notice here. 



The examination of two large colonies of the F2 generation of the cross lanuginosus x 

 praecox shewed that there were present m each, two distinct RR types (Figs. 7 and 10, 

 PI. XVI.) and three Rr types (Figs. 25, 26 and 27, PI. XV.). The difference in the degree 

 of ray development is due doubtless to the presence or absence of the hair factors. 

 Comparison of the figures 25, 20, 27, and of the figures 3, 4, 7, 8, 9, 10, and 11, will 

 prove that the character due to the presence of the same factor may be a variable one. 



The examination of the F^ generations of the cross lanitfiinosits x muIticauUs, in the 

 current year (1912), led to the conclusion that the four types of hairiness referred to as 

 Hi,, Hi, H-i, and i/3 are mainly due to the existence of three factors for hairiness. In 

 addition to H and Y there is a third factor which made itself evident by certain colonies 

 from a H-^ parent segregating in tlie proportion ffj : Hj :: 3 : 1. Ho, Hi, and H-^ plants 

 do not segregate apparently; Hiy = hh, Hi = HHDD, where D represents the third hair 

 factor, H3 = HHyy. ifj ni^y be homozygotic and is then probably always ffif IT. It is 

 often heterozygotic, and may throw either H\ or i/3 plants, but not both, in the proportions 

 //] : Ko :: 3 : 1 or i/o: JI3 :: 1 : 3. It must not be forgotten that other factors apparently 

 infiuence the development of hair (see p. 263). 



Fig. 1. Praecox. 45 days old, photographed as it commenced to flower. The neck of the 

 flask seen in Figs. 1, 2, and 3 is 26 mm. in diameter. The whole plant is practically 

 glabrous. 



Fig. 2. Lanuginosus. 103 days old, photographed as it commenced to flower. The whole 

 plant is very hairy. The flowers are not easily recognisable in the illustration. Most 

 botanists will, I think, be prepared ultimately to concede specific rank to the two 

 types shewn in Figs. 1 and 2. 



Fig. 3. One of the H2 types of Exp. 67, specially remarkable for the peculiar character of 

 the rays, which were originally recorded as Rr? but proved to be RR. A single head 

 is shewn enlarged as Fig. 11. It will be noted that the plant differs in other respects 

 from praecox and lanurjinosus. 



Figs. 4, 5, and 6. Microphotographs of single capitula of mufticauUs, radiatus, multicaulis, 

 radiatus x ynulticaulis, and multicaulis. Kadiate and non-radiate forms, if glabrous, 

 produce in all the generations one type of heterozj'gote only, that represented in Fig. 5. 

 All the microphotographs in Plates XV — XVIII, are magnified about four diameters. 



Figs. 7, 8, and 9. The radiate forms ol praecox, erectus, and generensis. 



Fig. 10. Capitulum of lanuginosus. 



Fig. 11. Capitulum with peculiar RR rays, liable to be mistaken for the Rr type. Com- 

 pare this with Fig. 25, which is that of a Rr head. 



Figs. 12, 13, 14, and 15. Side views of capitula of multicatdis, praecox, erectus, and 

 genevensis to shew size and shape of capitula and normal length of styles. Such types 

 set seed freely when selfed. 



