Vernalization and Photoperiodism — 70 — A Symposium 



is produced in an inactive form and that this inactive form after it reaches 

 a certain concentration limits the production of more of the inactive form. 

 The production of the active form presumably takes place, in short-day 

 plants, only during darkness by a process which is sensitive to temperature 

 and inhibited by light. In long-day plants the light inhibition of the change 

 to active form is presumed to be weak or completely absent. 



The evidence that has accumulated for the existence of a flower form- 

 ing hormone is sufficient to warrant a great deal more work in an attempt 

 to discover just what it is. If there is a single substance, or relatively few 

 substances of similar chemical nature, whose presence in the meristem de- 

 termines the course of development from the vegetative to the flowering 

 condition in all plants, the importance of discovering the chemical nature 

 of this substance or substances is obvious. The possible practical im- 

 portance of such a knowledge cannot be overemphasized. In view of the 

 encouraging nature of the results to date, it seems strange that there are 

 not more plant physiologists actively engaged in this field of research at 

 the present time. It is hoped that this present symposium may encourage 

 additional investigators to undertake work in this fascinating field. 



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