Alternating Annnal and Biennial Habit. 295 



Conversely many perennial plants which under nor- 

 mal conditions llower 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 

 ])erennial species are treated in horticultural practice ?is 

 annuals, and I myself have cultivated a whole series of 

 plants more or less regularly as such ; for instance, 

 Achillea Millefolium, Hesperis niatronalis, Lychnis z'cs- 

 pertina glabra, Picris hieracioides, Trifoliuni pratense 

 quinquefoliuni 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 biennis 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 s])ecies in cjuestion 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 Gernianicae et Heheticae (3d ed. 1857) and Gre- 

 NiER and GoDROX in the Flore de France (1852) give 

 Dipsacus syh'cstris 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 



