2 PJiijsiolofjical Predetermination 



is subsequently equalised during the main period of growth, and it is 

 directly reflected in the final yield. 



In the light of evidence afforded by growth curves based on dry- 

 weight measurements which were available in the literature, growth 

 and development within the limits of hereditary potentialities were 

 treated as fundamentally matters of physiological pre-dctermination. 

 The general expression covering growth was described as the Compound 

 Interest Law of Development. The operation of this law may be subject 

 to a number of secondary modifications. 



A few fundamental principles are necessary for the study of growth 

 and development. These are conspicuous by their absence in existing 

 text-books of plant physiology, which excel in the assemblage of 

 interesting curiosities and of uncorrelated details. The phenomena of 

 normal groivlh seem to call for further study and analysis and for the 

 application of mathematical treatment. Even a clear grasp of the 

 general conception of the compound interest law of development at 

 once greatly simplifies the handling of problems of physiological pre- 

 determination and of growth. One is able to formulate approximately 

 the magnitude of effects that will be observed as the result of causes 

 operating continuously or for a short time in relation to the stage of 

 development at which the cause operates and the effect is desired. 



In the cases with which we dealt in the preceding chapter the absolute 

 magnitude of the final effects upon yield were out of all proportion to the 

 absolute magnitude of the causes to which they were due. These causes 

 operated for a short period during the early stages of development and 

 initiated what we have termed physiological pre-determination. It is 

 this fact which makes the phenomenon of physiological pre-determina- 

 tion of such importance from the economic point of view. Roughly 

 speaking, the absolute value of the effect produced is proportional, not 

 to the value of the initial cause {i.e. that which has to be supplied by the 

 agriculturist), but to the value of the initial cause multiplied by the time- 

 interval between the operation of the cause and the reaping of the result. 



In the present chapter we deal with seed-treatments which we have 

 classified for convenience under the following headings, viz. : 



(1) Physical treatments of the seed ; 



(2) Chemical treatments of the seed, which do not obviously aftect 

 its nutrition 1. 



' It sliould lie pointed out that tlioro arc irifiny pajicis wliicli (ii-al with tlio cfTort upon 

 gcrmlnalioti of \ariou.s (•hciiiic-al trcatincnts of soods, but in which no inontion is made of 

 the pre-determining effects of the seed-treatments (cf. Bokorny (4); Siginund (32)). 



