33 
its mutative period. Furthermore forms not definitely assignable 
to any of the known mutants of this parent were found, showing 
that the range of the mutability of the species had been extended 
by unknown causes, but which were included in an environment 
of cultural conditions extremely favorable to rapid and vigorous 
growth and development. It seems safe to assume therefore that 
Fic. 11. One of the ie of the hybrid between Lamarck’s evening-primrose and 
mmon evening primrose (No. 2.24) 
the origination of species is induced, or at least increased by 
favorable, not adverse conditions, although the duration of the 
experiments has not been sufficient to permit an analysis of this 
phase of the subject. 
O. gigas, the species most recently tested in the mutation cul- 
