Translocation of Flowering Hormones • 73 



the plant, below the first, and exposed to long days without any 

 other treatment. Hence the inhibition of flowering was not due 

 simply to lack of carbohydrate transport through the chilled petiole, 

 since carbohydrates were still supplied by the long-day leaf, but to 

 the inhibition of the transport of the stimulus specifically from the 

 short-day leaf. These and similar results indicate that transport is 

 the result of cellular activity. Further circumstantial evidence im- 

 plicates the phloem in florigen transport by indicating that the 

 latter is associated with the movement of carbohydrates in the 

 plant. This evidence is not unequivocal, and is based largely on 

 experiments dealing with the effects of noninduced leaves on the 

 flowering response. 



Note that in Chailakhyan's experiment with Chrysanthemum, 

 discussed earlier, the upper portion of the plant was defoliated in 

 order to demonstrate the movement of a flowering stimulus from 

 the lower leaves on short days. Many observations, including those 

 of Chailakhyan, indicate that in some plants translocation can only 

 be demonstrated in this manner. A technique often used to study 

 this sort of question involves the use of two-branched plants, 

 produced by removing the apical portion of seedlings and allowing 

 two approximately equal lateral branches to develop. One branch 

 can then be exposed to inductive conditions, making it the donor 

 of flowering stimulus, and the other, on noninductive conditions, 

 is used as the receptor. When Biloxi soybeans are used in this way, 

 the receptor (long-day) branches flower only if they are defoliated 

 but not if the leaves are left in place, even though the donor 

 branch flowers well whether or not the receptor has leaves (Borth- 

 wick and Parker, 1938b). Similar results have been obtained in 

 other plants but are by no means universal. In the SDP Amaranthus 

 caudatus, defoliation of the receptor (long-day) branches greatly 

 inhibits, rather than promotes, their flowering, which is otherwise 

 almost as rapid as that of the donor branch itself (Fuller, 1949). 



Noninduced leaves can be kept in total darkness, rather than 

 removed, in order to avoid their inhibiting transmission. This 

 observation was actually first made by Garner and Allard in 1925; 

 the only reason they are not generally credited with the discovery 

 of the translocatable effects of photoperiodism is that they them- 

 selves stressed the localization of such effects in Cosmos, the SDP 

 they chose for work on this question. In this as in many other 



