Atavism by Seeds and Buds. 107 



this is true not only of those cases in which tlie cause 

 of the reversion is perfectly plain, but still more of those 

 in which the facts observed may lead us to suspect a cross 

 either in the previous generation or in more remote years. 

 By excluding such cases, however, the apparent abun- 

 dance of data relating to experimental atavism is very 

 much reduced ; l)ut it is obviously better to build on a few 

 reliable facts than on the highly insecure basis formed 

 by the numerous data which have hitherto been collected. 



With these reservations I shall now turn to the dis- 

 tinction between physiological and phylogenetic atavism. 

 Each has its own sphere. The object of the study of 

 the former is to discover the laws to which this form 

 of variation conforms. That of the latter is to discover 

 the ancestors of the species in question either by the ob- 

 servation of chance deviations, or by cultures and selec- 

 tion. 



Heinricher's extensive studies in the genus Iris 

 show how fruitful may be the application of selection 

 in the study of phylogenetic atavism.^ The cultivated 

 plants of this group are wqW known to be highly variable, 

 and the favorite Iris Kaeinpferi with its large flowers 

 affords numerous opportunities for the study of tetram- 

 erous and pentamerous flowers and of other variations. 

 Heinrichfr, starting from occasional anomalies pre- 

 sented by Iris pallida, and working on a methodical sys- 

 tem of selection, has raised an atavistic race which he 

 calls Iris pallida ahaviar The individual anomalies could 

 not, it is true, be fixed although they w^ere selected for 

 three generations, but a series of new types gradually 



* Carriere, Production et fixation dcs varictcs, 1865, p. 65. 



^ E. Heinricher, Versuche iihcr die Vercrbung von Rilcksclilags- 

 crschcinungcn. Jahrlx f. wiss. Bot., Vol. 24, Part I, 1892, and Iris 

 pallida abavia in Biolog. Centralbl., Vol. XVI, No. i, p. 13, 1896. 



