THE PRINCIPLE OF AEEANGEMENT. 41 



inasmuch as the law of alternation is thus carried out 

 completely, and which may be represented as follows — the 

 hyphens indicating the parts superposed to one another — 

 Sepal-stamen ; Petal-carpel. 



Prom what has been stated above, the true order of 

 arrangement and superposition would be — Sepal-stamen- 

 carpel; Petal-stameit-carpel ; and either one of the staminal 

 and either one of the cai-pellary whorls may be suppressed. 

 Thus, for example, Oxalis, Zygophylliim, Geranium, and Euta 

 have Sepal-stamen ; Petal-stamen-carpel : while Limnanthes, 

 Coriarea, and Agrostemma have Sepal-stamen-carpel ; Petal- 

 stamen. As instances where there is but one whorl of sta- 

 mens. Campanula and Hermannia have Sepal-carpel; Petal- 

 stamen ; whereas Idnum and Biosma have Sepal-stamen ; 

 Petal-carpel. 



Of these variations, although Sepal-stamen is commoner 

 than Petal-stamen, and Petal-carpel than Sepal-carpel,* 

 yet these are, so to say, rather matters of accident than 

 otherwise, in that it is probably due to certain exigencies of 

 nutrition, and especially insect agencies, that such variations 

 of arrangement exist 



The important fact mentioned above, that floral whorls 

 are projected cycles and not primitive whorls, has, as far as 

 I know, been entirely overlooked by botanists. Thus, for 

 example, Professor Asa Gray remarks on the presence of 

 whorls in flowers as follows : " Cycles alternating with each 

 other are simply that of verticillate phyllotaxy," f to which 

 he refers the opposite, temate, quaternate and quinate verti- 

 cils. J In the case of leaves, verticils represent usually more 

 primitive types, such as twos and threes, and, from an 

 evolutionary point of view, sxxcla. precede alternate and spiral 

 arrangements. 



• I.e. in Bxogens. t Bot. Text-Book, p. 175. % i.e., p. 120. 



