Sircar — 123 — In the Tropics 



this variety is reflected in the curtailment of vegetative growth of the main 

 shoot, which bears 10 leaves as against 16 in the control. It is interesting 

 to note that such a reduction in the flowering duration has only been no- 

 ticed in the main shoot which received the photoperiodic exposure, while 

 in the first and second tillers flowering was progressively delayed and in the 

 remaining tillers ear emergence was at about the same time as in the control 

 tillers. On the basis of the hormonal theory of development (K. C. Hamner 

 and J. Bonner, 1938, M. H. Cailahjan, 1936) an explanation for the va- 

 riation in the flowering times of the main shoot and tillers is suggested. It 

 appears that the flowering behaviour of the main shoot and tillers is related 

 to the distribution of flower-forming hormone in the growing points. Hor- 

 mone synthesized in the leaves exposed to short days was first translocated 

 to the growing point of the main shoot and induced flowering ; in addition, 

 a portion of it accumulated at the growing points of the buds formed at the 

 time of photoperiodic exposure. When these buds grew into tillers, accumu- 

 lated hormone caused their flowering, while the tiller buds formed after the 

 period of exposure received very little of the hormone, and consequently 

 their flowering was as late as the control. Thus it seems that the distribu- 

 tion and concentration of flowering hormone, florigen, could be the cause of 

 the variation in the flowering of the main shoot and tillers of the winter 

 paddy, Rupsail. The whole question requires further investigation on the 

 nature of the growing point at the time of photoperiodic exposure. 



In recent years the classification of plants into short and long day types 

 has been questioned by R. O. Whyte and M. A. Oljhovikov (1939) as 

 investigations on wheat, millet, rye and other cereals have shown that short 

 day or dark requirements of plants is inherent in the so-called short day 

 plants not throughout their life time but only during a definite period of 

 their development. After this period is completed short days tend to re- 

 tard subsequent development and long days are required. Accordingly 

 R. O. Whyte and M. A. Oljhovikov have concluded that so-called short 

 day plants are not typical short day plants but may be described as short 

 day — > long day plants. In winter rice a different picture is obtained (S. M. 

 Sircar, 1946). The acceleration of earing is maximum and grain yield 

 increased when Bhasmnanik seedlings are exposed all through to short days 

 and there is no succession of short and long days. Earing in the main 

 shoot of Rupsail is completed during short-day exposure for 6 weeks. After 

 this period long day treatment is found to retard flowering in the tillers for 

 which short days are necessary (S. K. Mukherjee, 1946). These results 

 indicate that winter rice completes its developmental phases under short 

 day conditions and is a typical short day plant. 



Wheat ( Triticum vulgare Vill. ) : — Failure of vernalization response to 

 pre-sowing low temperature treatment of early varieties of wheat was noted 

 by B. K. Kar (1940, 1942-43), and B. P. Pal and G. S. Murty (1941), 

 while B. Sen (1943-44) observed earliness in several late varieties from 

 North Western India. Although low temperature treatment failed to induce 

 earliness in B. K. Kar's experiments (1942-43), the treatment was effective 

 in inducing an increase in chlorophyll development of the leaves of young 

 seedlings, a greater output of tillers, a higher percentage of culm to tiller and 

 a greater flush of ear emergence. According to him, failure of low tem- 



