Effect of Ccitain Siibstonces on Growth and Floioering 



m 



Short-day plont 



Neutral plont 



Long-day 

 summer form 



O 



^ 



Sh 



^ 



L 



V 



Sh 



jCi> 



Long-day 

 winter form 

 L Sh 



G+A 



6+A GtA 



G + A 



Gibberetlins - hormones necessary for the stem formation. 

 Anthesines - hormones necessary for the flower formation. 

 Florigen= gibberellins + onthesines, necessary for flowering. 



Fif^. 1. Scheme of tormation of flowering hormones in various plant species. 



able for development, leaf samples were prepared with the aim of 

 extracting GA-like substances. Acetone was employed, and after 

 evaporation the dry residue was dissolved \\\ distilled water. 



Determination of GA-like substances by the growth reaction of 

 maize seedlings was performed by the method developed by Boyarkin 

 and Dmitrieva (1) in our laboratory. It was found that GA-like 

 substances were present in all tested extracts, there being more of 

 them in extracts from plants kept under long-day conditions than in 

 extracts from the leaves of plants kept under short-day conditions. 



The action of GA-like substances on the growth and flowering of 

 Rudbeckia was verified by the drop method for rosette plants sown 

 in the spring and kept under conditions of a short (9-hr.) day. A drop 

 of the tested extract, GA, or water was daily applied to the center 

 of the rosette of each plant. The experiment was carried out accord- 

 ing to the following scheme: (1) 0.02 per cent GA3; (2) an extract 

 from the leaves of long-day (L) 'Mammoth' tobacco; (3) the same 

 for a short-day plant (S); (4) an extract from the leaves of long-day 

 red perilla (L); (5) the same for a short-day plant (S); (6) an extract 

 from the leaves of long-day Rudbeckia (L); (7) the same for a short- 

 day plant (S); (8) the control, water. Four plants were used in each 

 experiment. The plants were treated during three months from De- 

 cember 9, 1958 to March 8, 1959. The experiment was completed on 

 April 4. 



As usual in plants treated with gibberellin, a fast reaction was 

 observed. They rapidly began to bud and flower, whereas up to the 



