532 M. Kh. Chailakhian 



On the other hand, consistent results have been obtained by many 

 authors and have indicated that GA accelerates flowering in many 

 long-day plants, including some winter forms and seedlings of bi- 

 ennials, but does not affect the flowering of short-day species (3, 4, 9, 

 10,11,14,16,17,18,20,22,30). 



Thus, an important problem was to clarify the relation between 

 GA and florigen. To tliis purpose we carried out some experiments 

 in 1957, together with L. I. Khlopenkova and T. N. Konstantino^■a 

 at the Institute of Plant Physiology of the USSR Academy of Sciences. 

 The influence of GA on the long-day species of rudbeckia (Rudbeckia 

 bicolor) and tobacco (Nicotiana silvestris), and on the short-day spe- 

 cies of red perilla (Perilla nayikinensis), 'Mammoth' tobacco (Nico- 

 tiana tobacum), and winter rape (Brassica napiis var. oleifera) was 

 studied. 



The results of these experiments led us to the conclusion (11) that 

 two sets of substances compose the flowering hormones, or florigen, 

 which are common to all plants. These are, on the one hand, GA, 

 which is necessary for the formation and growth of stems and, on the 

 other hand, some substances that are necessary for the formation of 

 flowers and which have tentatively been called anthesins. From this 

 standpoint the absence of flowering of long-day species under short- 

 day conditions is explained by a lack of GA, whereas the absence of 

 flowering of short-day species under long-day conditions is ascribed 

 to anthesin insufficiency. Absence of flowering in winter forms and 

 in seedlings of biennials is due to gibberellin deficiency under long- 

 day conditions and to gibberellin and anthesin deficiency under short- 

 day conditions (Figure 1). 



This assumption, which is based on new facts concerning the in- 

 fluence of GA on the growth and development of plants and also on 

 data from grafting experiments, requires, of course, fmthcr experi- 

 mental and theoretical study. 



One proof of this hypothesis would be to extract GA-like sub- 

 stances from the leaves of short-day plants located under long-day 

 conditions and to induce, with the aid of these substances, flowering 

 in long-day plants located imder short-day conditions. A circum- 

 stance which facilitated the solution of this problem was that these 

 substances have been isolated from the seeds and unripe fruits of a 

 number of plants (5, 19, 21, 26). 



Together with V. N. Lozhnikova we carried out an experiment 

 (13) for extraction of GA-like substances from leaves of short-day 

 plants ('Mammoth' tobacco and Perilla), as well as of long-day plants 

 (Rudbeckia). The plants were cultivated under long (L) and short 

 (S: 9-hr.) days, and after buds began to form under a day length suit- 



