ii DEVELOPMENT AND ENVIRONMENT 51 



experiment if a result with a probable error of 

 + 1 '0 per cent, is to be obtained. 



The evidence to hand indicates that photosynthesis 

 takes place largely in the early morning, the subsequent 

 closure of the stomata preventing free access of C0 2 to the 

 chloroplasts. The curve of increase in dry-weight follows 

 the temperature curve till nine o'clock, and then the 

 stomatograph record, with differences in detail between 

 old leaves and young ones during the afternoon. 



The increase in dry-weight in hourly series of observa- 

 tions, without correction for loss by translocation, has 

 given record values at the highest point of the curve, 

 namely 25 (4) mg. per sq. decim. per hour. This rate 

 is reached in June, between 8 a.m. and 11 a.m., when the 

 stomata are at their maximum dilatation, and the tempera- 

 ture is above 30 C. There is reason to believe that values 

 of about 30 mg. may yet be obtained under certain con- 

 ditions, thus reaching the absorption of a surface of KOH 

 when exposed freely to the wind. 



It is improbable that the intensity of illumination should 

 ever be a limiting factor in the process, except before 

 sunrise. 



No definite signs of growth-limitation by deficient 

 photosynthesis have yet been discovered, unless in such 

 circumstances as the last three hours of Fig. 34, though 

 here again we ultimately may find some such effect in 

 the autumn. 



The first flower. The date of appearance of the first 

 flower on any individual plant deserves consideration in a 

 separate section ; being the ultimate result of a long series 

 of interacting factors, morphological and physiological, it 

 is in itself an automatic summary of their effects and it 

 possesses the additional distinction of being commercially 

 important. The " date of arrival of the crop " is almost 

 entirely dependent on the "first-flower date," but the 

 grower does not seem to realise that he is given nearly two 



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