52 Pctch : Xotes on Aster tripoUiiiu. 



majority of the flowers are rayed may have two or three stems 

 of discoid heads only. 



The arrangement of the capitula is ultimately cymose. It 

 freqiientlv happens that immediately behind the leading- flower 

 (a) there grows a younger and less conspicuous one (b). In 

 these we have such numbers of florets as the following :— (a) 

 II ray + 27 disc, (b) o ray + 22 disc; (a) 9 ray + 20 disc, (b) 

 o ray + 18 disc ; (a) 18 ray + 27 disc, (b) 12 ray + 27 disc ; (a) 

 7 ray + 18 disc, (b) i ray 4- 18 disc. The second flower almost 

 invariably has fewer ray florets and generally fewer disc florets. 

 But how such difference can be induced on different stems of 

 the same plant or in two plants growing close together is 

 inexplicable. 



Dr. MacLeod states (loc. cit. ) that the discoid head has ten 

 or more florets, while the rayed head has tw^enty to twenty-five 

 disc florets and fifteen to twenty rays. Specimens gathered on 

 the ' Humber shore were divided according to their general 

 appearance into rayed, non-rayed, and intermediate. The heads 

 of the rayed plants contained 10-30 rays and 18-38 disc florets ; 

 the intermediate contained 0-16 rays and 18-31 discs ; while the 

 non-rayed heads consisted of 8-25 disc florets. An examination 

 of several hundred flowers showed that there was a wide varia- 

 tion in the number of florets per head and their division into 

 disc and ray among the flowers of a single plant, but that the 

 well-rayed flowers were less variable than the intermediate form. 

 Thus, rayed flowers on the same plant vary from 19 rays +25 

 discs to 30 rays + 31 discs ; 17 rays + 20 discs to 21 rays + 30 

 discs ; 13 rays + 19 discs to 17 rays + 23 discs ; while the 

 intermediate plants vary from o rays +17 discs to 16 rays + 29 

 discs ; 2 rays + 21 discs to 14 rays + 31 discs ; 2 rays + iS 

 discs to 13 rays + 21 discs. In general a rayed head, no matter 

 how few the rays, possesses more disc florets than a discoid 

 head ; and an increase in the number of rays is accompanied by 

 an increase in the number of disc florets. The maximum 

 number of florets in a head was 66, 28 rays + 38 discs ; the 

 niunber of disc florets exceeds the number of rays in most cases, 

 a few exceptions occurring with the higher numbers of ray 

 florets, e.g., 31 rays + 31 discs. 



An analysis was also made of disc and rayed heads taken at 

 random from the same and different plants. In one head con- 

 sisting of 18 ra\ s + 27 disc florets, the ray florets showed the 

 lengths, ovary 1-6-2 mm., tube 3'5-4 mm., limb 9-10 mm,, and 

 breadth of limb i'5-i-8 mm. The disc florets were 8*5-1 1 "5 mm. 



Naturalist, 



