Vernalization and Photoperiodism — 66 — A Symposium 



to it, even though the grafted leaf was placed on long day. Long (22) 

 obtained similar results with Xanthiiim. Cailahjan concluaed that the 

 flower hormone accumulated in the leaves of plants exposed to short day 

 and that it was used up in flower bud and flower formation. Hamner 

 and Bonner (16) obtained evidence with Xanthium that the continua- 

 tion of the supply of the stimulus subsequent to a short-day treatment was 

 not due to simple storage of the stimulus during actual exposure to short 

 day but to a continuing generation of the stimulus after short-day treat- 

 ment was discontinued. Moskov (31) with Perilla reaches similar con- 

 clusions. Other short-day plants do not seem to continue to supply the 

 stimulus after the short-day treatment has been discontinued. With 

 Biloxi soybeans, Long (22) found that two periods of flowering would 

 result after exposure to two short-day induction treatments occurring 

 about two weeks apart. Botvinovskii (4) obtained similar results with 

 hemp. Thus, a given induction treatment resulted in a certain flowering 

 response and the effect then disappeared. 



There is some evidence that the stimulus for flower initiation is used 

 up in the actual process of flower formation and floral development. 

 Hamner and Bonner (16) with two-branched Xanthium plants found 

 that the stimulus was received with greater force by the receptor branch 

 (maintained on long day) when all buds of the donor branch (exposed to 

 short day) were removed. It would be of interest to determine whether 

 or not the stimulus would be stored provided there were no buds avail- 

 able to use it up. 



The transmission of the stimulus longitudinally through a stem of a 

 short-day plant from a leaf exposed to short day to an actively growing 

 bud is in some way inhibited or partially inhibited by the presence on the 

 stem of mature leaves exposed to long day. Cailahjan and Jarkovaja 

 (9) with Perilla found that the removal of such leaves increased the trans- 

 fer. Hamner and Bonner (16) with Xanthium demonstrated that the 

 receptor branch of a two-branched plant, one branch on long day and the 

 other branch on short day, did not flower provided the young leaves were 

 removed and the older, mature leaves remained attached to the receptor 

 branch. With no defoliation or with complete defoliation, the receptor 

 branch flowered. Thus, there were indications that young, developing 

 leaves exert a promotive eflfect on the transmission of the stimulus which 

 more than counterbalances the inhibitory effect of mature leaves. Borth- 

 wiCK and Parker (1) with two-branched Biloxi soybeans, one branch on 

 long day and the other branch on short day, found that the receptor branch 

 initiated flowers provided its leaves were removed. Heinze, et al., (18) 

 with Biloxi soybeans found that defoliation of a receptor plant of graft- 

 partners increased the response of the receptor. Moskov (30) found 

 that the receptor components of grafted plants responded more satis- 

 factorily if the leaves were placed in complete darkness rather than in long 



day. 



The stimulus is transferred readily across a graft-union. Moskov 

 (25), in his early work from which he first concluded that there was trans- 

 fer of a stimulus, used two varieties of tobacco, Maryland Mammoth and 

 Sampson. The Maryland Mammoth tobacco is a typical short-day plant. 



