V. ATAVISM. 
12. ATAVISM BY SEEDS AND BUDS. 
HOFMEISTER in his Allgemeine Morphologic defines 
atavism in these words : "The occurrence of reversions, 
the offspring of a variety of known origin resembling 
the parent type" (p. 559). 
According to the meaning of the word "known" in 
the above definition the term atavism may embrace quite 
a series of phenomena of the most diverse importance. 
It may mean either that this origin must have been actu- 
ally observed, or that it can be inferred with sufficient 
certainty from comparative and systematic studies. If 
we are merely dealing with morphological questions this 
distinction may appear unessential, but as soon as our 
object is to test by experiment the results obtained, it 
becomes of the highest importance. For to obtain true 
experimental proof of atavism it is obvious that the 
origin of the forms should be known directly by observa- 
tion. 
The origin of a whole series of varieties and ele- 
mentary species from their parent forms, however, is 
sufficiently established by the historical evidence relating 
to their first appearance. It seems therefore feasible to 
confine our attention to such cases and to draw a distinc- 
tion between physiological and phylogenetic atavism. The 
former is reversion to actually known ancestors, the latter 
to systematic ancestors. 
