PREDETERMINATION 187 



an almost untrodden field, and some of the results observed 

 may be ascribed to individual peculiarity rather than to this 

 or to that factor. 



Gregory,* in his study of the effect of climatic conditions 

 on the growth of barley, recognizes eight environmental 

 factors : maximum day temperature, average day temperature, 

 minimum night temperature, average night temperature, total 

 radiation in calories per sq. cm. per week, hours of bright 

 sunshine, evaporating power of the air and the nitrogen factor, 

 which is important in the rate of growth of the leaf. 



Allusion has been made to the importance of the previous 

 history of the conditions and of the plant in determining 

 the activity of the plant at any moment. In the present 

 connection, the important and extensive work of Balls on the 

 cotton plant must be mentioned. | From a long series of 

 observations, Balls concludes that the different behaviour of 

 the plants, as indicated by the crop of cotton, are the inevitable 

 consequences of the known environmental conditions, pro- 

 vided that proper regard is paid to the distinction in time 

 between the incidence of the conditioning factor and its mani- 

 festation in the crop. Thus the daily fluctuations in the 

 flowering curve are predetermined and controlled by the 

 weather conditions which obtained a month before the flower 

 opens. This is the principle of predetermination : its im- 

 portance is obvious ; an accurate knowledge of predetermining 

 factors will amongst other things give to certain aspects of 

 physiology, ecology, and agriculture a precision which now is 

 sometimes lacking.^ 



THE CONDITIONING FACTORS. 

 Temperature. 



The factors which condition growth and its rate are pre- 

 cisely those which influence anabolic and catabolic activities, 



* Gregory : " Ann. Bot.," 1926, 40, 1. 



f Balls : " Phil. Trans. Roy. Soc," B, 1917, 208, 157. 



J For an application of this principle, see Appleman's paper on "Fore- 

 casting the Date and Duration of the Best Canning Stage for Sweet Corn " 

 (" Univ. Maryland Agric. Exp. Sta.," 1923. Bull. 254). 



