Murneek — 57 — Research in Photoperiodism 



or through dead petioles. When the bark is removed, there is no transfer 

 of the hormone (Cajlachjan, 1938, 1940, 1941 ; Hamner and Bonner, 

 1938; BoRTHWicK et al., 1941; Withrow and Withrow, 1943; Stout, 

 1945). 



The hormone moves up and down the stem with almost equal facility, 

 though the upward transport is the more common direction (Heinze et al., 

 1942). It may be stored to some extent in the stem and probably other 

 parts of the plant. Some believe that the hormone can be transferred 

 through an inert partition such as lens paper, inserted at the union be- 

 tween the two graft symbionts (Hamner and Bonner, 1938) though more 

 recent findings seem to show that its translocation between donor and re- 

 ceptor plants is possible only when there is established a direct union 

 (MosHKOV, 1939; Withrow and Withrow, 1943). 



The hormone moves to the terminal meristems where in some unknown 

 way it aflfects the apical cells changing their activity from production of 

 vegetative tissues to inception of floral primordia. Not all of the meristems 

 are in the same stage of development at any particular time of induction, 

 or perhaps do not get the same dosage of the stimulant or else are not 

 equally susceptible to it. Those nearest to the photoperiodically most sensi- 

 tive leaves may perchance receive the hormone sooner or in larger amounts 

 than the more distant ones, for when buds nearest to the functional leaves 

 are removed other buds seem to get more of the catalyst. Borthwick and 

 Parker (1938) have shown that the first microscopically visible response in 

 the Biloxi soybean, as a result of exposure of the whole plant to 5 or 6 

 short days, was in the buds located in axils of leaf primordia that were 

 fourth or fifth from the tip of the main stem. Harder et al. (1942) think 

 that in meristematic regions the hormone is distributed throughout the 

 tissue, but even here there may occur a one-sided effect. The production 

 of flowers with only partial expression of the reproductive organs and asso- 

 ciated tissues, already referred to, would seem to suggest an incomplete 

 supply of the hormone to meristems from which they arose or else inter- 

 ference at some later stage in flower development. 



"Photoperiodic 



inoucHon, 



n — *rn 



Tgrminal veoetative Barty siage of repro- 



meristem, ducHve meristera. 



One of the crucial aspects of the photoperiodic induction of floral 

 primordia unquestionably is the first changes in the vegetative meristems, 

 more accurately the retardation in multiplication of the apical cells. It is 

 well known that the first microscopically observable alteration at the 

 rounded tip of the meristem, that changes toward the formation of repro- 

 ductive tissues, is the formation of a plateau. The meristematic cells are 

 inhibited at X. It would seem to be very desirable to conduct detailed 

 cytological and possibly microchemical studies of the meristem during the 

 earliest changes toward reproduction as effected by the photoperiod and 



