Atavism by Seeds and Buds. 107 
this is true not only of those cases in which the 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 ; but 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. 1 The cultivated 
plants of this group are well known to be highly variable, 
and the favorite Iris Kaempferi 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 abavia. 2 The individual anomalies could 
not, it is true, be fixed although they were selected for 
three generations, but a series of new types gradually 
1 CARRIERE, Production et fixation des varictcs, 1865, p. 65. 
2 E. HEINRICHER, Versuche ilber die Vererbung von Riickschlags- 
erscheinungen. Jahrb. f. wiss. Bot, Vol. 24, Part I, 1892, and Iris 
pallida abavia in Biolog. Centralbl., Vol. XVI, No. i, p. 13, 1896. 
