3 2 BOTANICAL GAZETTE [january 



The horsechestnut is not peculiar in this respect, and further con- 

 siderations, with regard to compound leaves generally, have confirmed 

 in my own mind my first understanding of the matter. Disarticula- 

 tion of the leaflets seems to be universal in deciduous-leaved species. 

 It occurs in many families separated in a natural system by entire- 

 leaved groups, as in Juglandaceae, Berberidaceae, Anonaceae, 

 Rosaceae, Rutaceae, Sapindaceae, Vitaceae, Oleaceae, Bignoniaceae, 

 Caprifoliaceae. That is, it must have arisen in evolution many times 

 independently. There must, then, be 



some 



ciple capable of bringing the disarticulation in question to light, 

 wherever compounding of the blade establishes the conditions for its 

 operation. This principle seems, as has been argued above, not to 

 be natural selection. There is, however, in plants a recognizable 

 principle of morphic translocation, mobility of characters, or homoeosis 

 (Bateson), to which the phenomenon may very well be referred. 1 

 The conditions favorable to its operation in this case are very obvious, 

 since the structural relations at the junction of the petiole and stem 

 are imitated at the junction of petiolule and petiole (or rhachis). 



The Pierson fern 



Recently evidence corroborating the above interpretation has 

 come to hand in a case where advance in complexity has been all 



mutation 



out pernaps 1 am using the word somewhat loosely, if the DeVriesian 

 sense is to be insisted upon. The plant is the Pierson fern, now well 

 known to horticulturalists and to the public generally. The meta- 

 morphosis of the Boston fern, to which the Pierson owes its origin, 

 seems not to have been hitherto described as a 

 formation ; yet such it is. 



homoeot 



small 



— . WMV , yas 1UUUU wnne u was still smau, 

 among vegetatively propagating Boston ferns in the greenhouses of 



Mr. F. R Ptttbc^xt *u„ —n i .. . .. * 



N 



appeared fn"lStoV M xT' ""^ "° n translocati * n <* characters in plants," 

 that Bateson had briefly treaL £?« I9 ° S \. When k wa * written I did not know 

 and had devised the ^E^ TfiS^t 5 """T 5 **?" ° f anlmaIS 

 pose and more convenient to use than my own %££*****' * *" <"■"* PUF " 

 • Mr. F. R. Pierson, in a letter to the writer. 



