Translocation Rate • 77 



In certain plants, such as the SDP Piqueria trinervia (stevia), 

 the effect of inductive treatment remains relatively localized no 

 matter what manipulations are performed (Zimmerman and Kjen- 

 nerud, 1950). Thus the only summary statement that can be made 

 about the movement or apparent movement of flowering hormones 

 is that it takes place in living tissue, probably through the phloem; 

 that it can be either acropetal (base to apex) or basipetal; that it 

 may be localized or systemic depending on the plant, the structure 

 of its vascular system, and the condition of noninduced portions. 

 There is evidence that noninduced leaves act in an inhibitory 

 fashion primarily but not exclusively by affecting the predominant 

 direction of carbohydrate movement, with which the florigen may 

 be carried. 



TRANSLOCATION RATE 



There are very few studies on the rate of movement of floral 

 stimuli, again because of the difficulty that only the final response, 

 not the postulated hormone, can be measured. Early work by 

 Chailakhyan suggested values of about 2 cm in 24 hours in Perilla, 

 but it is doubtful whether conditions were optimal (see Lang, 

 1952). Some ingenious experiments by Imamura and Takimoto 

 (1955b) provide the best data so far available. 



Plants of the SDP Pharbitis nil (Japanese morning glory) can 

 be reduced to a stem with a single leaf, and then decapitated so 

 that the bud in the axil of the leaf will start to grow. The position 

 of the first flower on the axillary shoot will then depend on the 

 time between the start of growth (decapitation) and the start of a 

 single 16-hour inductive dark period given to the leaf. In one 

 experiment, for example, if the dark period was started imme- 

 diately after decapitation, the average position of the first flower 

 on the axillary shoot was at node 2.8 (that is, node 2 in some 

 plants, node 3 in most). If 24 hours elapsed between decapitation 

 and the dark period, the average position was node 3.5, and so on. 

 Such differences are developmental expressions of the amount of 

 time during which the axillary bud (shoot) was growing before the 

 flowering stimulus reached it. Parallel experiments can be done at 

 the same time with plants in which the distance between the single 

 leaf and the receptor bud is greater-for example, by having the 



