CYCLIC MANIFESTATION OF STERILITY IN BRASSICA 
PEKINENSIS AND B. CHINENSIS. 
A. B, SToUr 
(WITH SEVEN FIGURES) 
The transition from asexual or vegetative growth to the con- 
dition of flower and fruit production in hermaphrodite plants is 
to be recognized as a most fundamental aspect of sexuality. 
Furthermore, the inter-relations that exist between vegetative and 
reproductive vigor and the influence of the former on the latter 
are reflected and exhibited in certain phenomena of sterility. 
It is now certain that vegetative vigor and the internal inter- 
relations incident to it may limit reproductive vigor and sexuality. 
The limitation from these causes may take place in two ways: (1) 
they may interfere with or influence the morphological development 
of flowers or other reproductive organs, and (2) they may affect the 
functioning powers of organs that are fully formed. If these influ- 
ences are marked, one or more types of sterility may appear. 
Only recently observations have indicated that, at least in 
some cases, the compatibilities and the fertility of the sex organs 
may vary rather definitely within the cycle of vegetative and 
reproductive development characteristic of the particular species. 
A phenomenon of this sort is reported by East and Park (4), 
who found that in the few plants which are self-compatible in 
certain species and hybrids of Nicotiana, the self-compatibility 
develops only at the end of the flowering period. Cases of cross- 
compatibility appearing only at the end of the period of bloom are 
reported also. A very decided case of the development of self- 
compatibility only at the close of the period of bloom was observed 
by the writer, in a plant of Lythrum Salicaria, and reported at the 
annual meeting of the Botanical Society of America for 1917. 
These observations suggested that new evidence on the old problem 
of the relation between vegetative vigor and reproductive vigor, 
as expressed in the formation of flowers and the functioning of the 
Botanical Gazette, vol. 73] [ar 
