74 • Floral Hormones and thf. Induced State 



plants, flowering in normal, intact individuals is confined to the 

 area exposed to induction. A portion of the plant kept in total 

 darkness, however, will exhibit a flowering response, provided an 

 adjacent portion is kept on inducing (short-day) conditions. An 

 elegant experiment by Stout (1945) illustrates the same situation 

 for an LDP, the sugar beet (Beta vulgaris). Plants with three shoots 

 were made by root grafts. If one of these shoots was exposed to 

 long days, it flowered and also brought about flowering in a second 

 shoot kept in darkness. The third shoot, however, maintained on 

 short days, remained vegetative. 



As suggested earlier, most experiments of this kind can be 

 interpreted as indicating that florigen moves in the prevailing 

 direction of carbohydrate movement. In this view, darkening or 

 removing leaves from a noninduced part of the plant results in a 

 lower carbohydrate production in that part, so that carbohydrate 

 (and florigen) movement in its direction is increased. There are 

 alternative explanations, however, as will become evident later. In 

 some cases, darkened leaves may inhibit translocation; this has 

 been interpreted as a "diversion" of the movement into such leaves 

 (see Lang, 1952). 



Interesting evidence on the translocation of floral hormones 

 and the effects of noninduced leaves comes from work on the SDP 

 Kalanchoe blossfeldiana reported by Harder (1948). With a mini- 

 mal short-day treatment, development of the complex, branching 

 inflorescence is slow and "vegetative"; that is, the flowers are small 

 or abortive and the bracts among them overdeveloped and leaflike. 

 If only a single leaf receives short-da y treatment, inflorescence 

 development may be normal, provided the treatment continues 

 long enough; but commonly it is notably asymmetrical, being more 

 normal on the side directly above the induced leaf and vegetative 

 on the side away from it (see Fig. 5-2). Examination of the vascular 

 svstem shows that this is consistent with the idea that florigen 

 simply moves in the phloem: the lateral connections in Kalanchoe 

 are relatively minor, so that little lateral movement of the effect 

 would be expected. 



Experiments on the effects of noninduced leaves in Kalanchoe 

 depend on its decussate leaf arrangement; that is, each pair of 

 opposite leaves is at right angles to the pair above or below it. 

 Thus looking down on the plant one sees four ranks of leaves at 



