Hamner — 69 — Hormones 



leaves is regrafted to the plant near the growing point, the plant does not 

 flower unless the leaf is exposed to long day. Exposure of an intact plant 

 to a low temperature even under short day results in flowering. Infiltra- 

 tion of the leaves with sugar also results in flowering. 



Lang and Melchers consider that the annual form and the biennial 

 form subsequent to vernalization fail to flower under short-day conditions 

 because of the removal by the leaves of substances which would ordinarily 

 result in flowering {i.e., a flower-forming hormone). This restrictive in- 

 fluence of the leaves becomes operative only during long, dark periods 

 and apparently is related to exhaustion of carbohydrates in the leaves since 

 the infiltration of the leaves with sugar or the treatment of the leaves 

 with low temperature (a process which might conserve the leaf carbo- 

 hydrates) removes the restrictive influence. They subscribe to the theory 

 that flowering results from the transmission of a specific stimulus, "flori- 

 gen," to the growing point. In annual Hyoscyamits they believe that this 

 stimulus may be in some way continually supplied— perhaps from the roots 

 or stored in the stem during exposure to light and that during long, dark 

 periods the mature leaves remove this stimulus from the stem, and it does 

 not have an opportunity to accumulate in the growing point and result in 

 floral initiation. They speculate on a mechanism of response for all long- 

 day plants based upon the results obtained with the annual Hyoscyamits 

 niger. 



The results which have been obtained with Hyoscyamus niger have not 

 been obtained, as yet, with other plants. It was noted with several short- 

 day plants (see above) that mature foliage leaves in some way inhibited 

 the transfer of the flowering stimulus when they were exposed to an un- 

 favorable day length. The removal of such leaves often results in the 

 transmission of the stimulus from parts exposed to short day to other 

 branches maintained continually on long day. 



Cholodny (10) presents the hypothesis that auxin is involved in the 

 flowering processes and the various environmental factors through their 

 action on the synthesis and distribution of auxin determine whether or not 

 a given plant flowers. He reviews the various experiments which indicate 

 the possibility of a "flower-forming hormone." He believes that he could 

 find no evidence to rule out the possibility that auxins were involved in 

 the transition from vegetative to the flowering condition, although he in- 

 dicates that it may be possible under certain conditions that it is the lack 

 of auxin rather than the presence of auxin which causes this transition. 

 He states, "We must form no hasty conclusion regarding special 'organ- 

 forming substances' .... we must first test whether some of the already 

 known phytohormones are endowed with the faculty to induce the physi- 

 ological effect under observation. . . ." Other investigators have ques- 

 tioned Cholodny's hypothesis, and it seems to the author that experi- 

 mental evidence fails to give it much support. 



Chouard (U) believes the hormone of flower formation is distinct 

 from auxin. He was able to induce flower formation in the long-day 

 plant, China aster, growing under short days by applying dehydrofolliculin. 

 He postulates that the hormone of flower formation is synthesized in the 

 green leaves only under the action of light but believes that the hormone 



