Alternating Annual and Biennial Habit. 295 
Conversely many perennial plants which under nor- 
mal conditions flower the second year after germination 
for the first time, can be induced by favorable cultiva- 
tion to flower in the first summer, though this does not 
always succeed with every individual. In this way many 
perennial species are treated in horticultural practice as 
annuals, and I myself have cultivated a whole series of 
plants more or less regularly as such ; for instance, 
Achillca Millefolium, Hesperis matronalis, Lychnis i'cs- 
pcrtina ylabra, Picris hieracioidcs, Trifoliuni pratcnse 
quinquefolium and others. 
Let us proceed now to our more immediate subject, 
the phenomenon of the occurrence of many species partly 
in annual and partly in biennial specimens. Such plants 
are regarded by descriptive systematists as biennials, as, 
for instance, the name Oenothera bicnnis indicates; for, 
under the less favorable conditions which usually obtain 
in the field the great majority of the specimens will be 
biennials. 
In my opinion this view is quite correct, but the bien- 
nial species in question must possess the capacity of grow- 
ing as annuals, in a semi-latent condition. Moreover 
this capacity does not seem to be universal, but to be con- 
fined to particular races. For instance, KOCH'S Synopsis 
Florae. Gennanicae et Helveticae (3d eel. 1857) and GRE- 
NIER and GODRON in the Flore de France (1852) give 
Dipsacus sylvestris as an annual, whilst I myself have 
hitherto only been able to raise biennial races of it from 
seeds derived from numerous different sources, and in 
spite of the fact that I modified the culture in every con- 
ceivable direction in the hope of making them annual. 
It is highly probable that many species exist in certain 
