THE LOW TEMPERATURE PROMOTION OF FLOWERING 59 



and 100 fxg gave maximum effect. On the other hand, about 900 /xg 

 (5 /Ltg/day for 6 months) was only partially effective on parsley. It 

 is important to note that only 0.001 /^g/plant will give a significant 

 stem elongation response, and thus the doses required for promotion 

 of flowering are exceptionally high. 



The most impressive thing about this work is that a well-defined 

 pattern is evident in the results with many species : 



A. Flowering of many cold requiring plants with the rosette 

 form is promoted in the absence of cold treatment by application 

 of gibberellins, showing that gibberellins will substitute for a cold 

 requirement. If the plant also has a long-day requirement, effects 

 of gibberellins are best observed when plants are treated with the 

 chemical under long-day conditions. In a few instances such plants 

 have been made to flower with gibberellins in warm, short-day 

 conditions, but often this results only in stem elongation but no 

 flowering. 



B. Long-day plants without a cold requirement may often be 

 made to flower under short days by treatment with gibberellins. 

 In a long-short-day species of Bryophyllum, application of gibberel- 

 lin under short days promptly results in flowering, but application 

 under long days does not. Thus gibberellins can substitute for 

 the long-day requirement. 



C. Applied gibberellins do not cause flowering of short-day 

 plants under long-day conditions. There are a number of reports 

 of promotion in flower development by gibberellins in short-day 

 plants when the plants have been induced to flower by a short-day 

 treatment, but gibberellins by themselves do not seem capable of 

 substituting for short days. In some cases gibberellins inhibit the 

 flowering of short-day plants, but the particular response seems to 

 be strongly dependent upon the environment. 



D. There are a few cases where applied gibberellins do not 

 cause flowering of cold- or long-day-requiring plants. This is 

 especially true of such plants with a caulescent growth form (an 

 elongate stem instead of only a rosette of leaves). Indeed, virtually 

 all short-day plants are of this type. Gibberellin treatment may 

 also inhibit flowering of Petkus rye and other cereals when it is 

 applied to young plants, although application to older plants may 

 promote flowering. Rosette plants in which lateral buds become 

 reproductive while the terminal bud remains vegetative (e.g. Geum 



