Vernalization and Photoperiodism — 98 — A Symposium 



Like most of the anatomical studies reported in the Hterature, analytical 

 studies have been more commonly on samples from different environmental 

 treatments or of plants in later stages of flowering or fruiting rather than 

 of samples in early stages of sexual reproduction (9). To secure evidence 

 on the physiology of sexual regeneration, sampling of potentially flowering 

 plants should be done at the time of blossom induction. 



Similarly, cytological studies of the apical meristems involved in the 

 difTerentiation of floral primordia are needed. 



Role of Anatomy: — That no possible misunderstanding arise, it is 

 clearly acknowledged that the significance of the anatomical situations 

 which have been found to be associated with sexual reproduction is not 

 known. 



It is difficult, however, to avoid considering that the stopping of phloem 

 formation at the time of induction and prior to blossom difTerentiation and 

 flowering might not greatly affect transfer of the flowering stimulus as well 

 as conduction of other elaborated substances from the leaves.^ On the other 

 hand, the evidence is not now sufficiently definite to justify proposing that 

 anatomical conditions are causative in sexual reproduction, even though 

 the possibility seems to exist. 



Phytohormones : — The phytohormones have been considered as causal 

 in blossom initiation by numerous workers (chapter 6, this series). At 

 least, names have been proposed ("florigen" of Cajlahjan and "anthesin" 

 of Cholodny) for the as yet unextracted substance which is presumed to 

 pass through a graft union and cause the flowering of a receptor plant. 

 If phytohormones are the real stimulating agent they obviously work 

 through the mechanism which inhibits cambial activity and induces matura- 

 tion. This gives a clue as to the physiological reaction they would induce. 

 A substance which would result in maturation phenomena would be un- 

 like any commonly known phytohormone as the ones now available for 

 plant treatments induce proliferation. Should a "maturity inducer" be 

 isolated it should not only be of potential use in causing flowering but also 

 be a possible remedy for cancerous growths, that is, if cancer is "the inabil- 

 ity of cells to stop growing." Methods of extraction should be directed 

 toward the securing of such a substance. 



Relation with Photoperiodism : — Since anatomical conditions have 

 been seen to be correlated with sexual reproduction, it is very obvious that 

 a given photoperiod, as for example a short day, would not result in a 

 common anatomical situation in different plants as it would either induce 

 blossoming (of a short-day plant), inhibit blossoming (of a long-day 

 plant), or have little if anything more than a time effect upon blossoming 

 (of a day-neutral type). 



* From our observations, a transfer of the stimulus-to-flower by grafts separated 

 by a "diffusion contact" of lens paper (7) is not possible unless the proliferating tissue 

 has penetrated the separating medium and made a direct contact between the donor and 

 receptor stems as found by Moshkov (10) and by Withrow and Withrow (41). 

 MosHKOv reports a 10-day "physiological contact" is necessary to secure induction 

 with Perilla grafts. 



