GROWTH AND WATER USE OF VEGETABLES 



249 



fSOOr 



1000 



500 



• SPRING 

 o AUTUMN 



o o •* 



10.000 



I I I 1 I I 



20.000 



30.000 

 $ caL.cm ' 



Fig. 2. The relation between radiation- and heat-sum for different growth periods in 



(spring (•) and autumn (o). 



additive to one another, the following relation can be obtained from a 

 statistical analysis: 



■■A 



Txy = 0-92 



rxy = 0-94 



(I) 



(^) 



where Zf and za are respectively fresh- and dry-weight yeild and x and y, 

 total radiation and heat sum. The effect of heat sum (0-26 and 0-0434 with 

 fresh- and dry-weight respectively) seems to be higher than that of total 

 radiation (00903 and 0-00464 respectively). The real value of the latter, 

 under our circumstances, is 15 to 30 times that of the former (vide Fig. 3), 

 so the effect of radiation is many times larger than that of the heat sum. 

 In the application of heat sum and radiation it is supposed that the effect 

 on growth is linear and that minimum and optimum for growth are not 

 surpassed. Moreover, that there is no influence of day-length, whereas the 

 effect of day and night temperature is assumed to be the same. Though 

 these suppositions are not exactly true, a fairly hnear relationship was 



