250 



J. F. BIERHUIZEN 



obtained, which is at least partly due to the fact, that favourable and 

 unfavourable conditions balance each other over the growth period. 



Photosynthesis experiments carried out by Bohnig and Burnside (1956) 

 and by Gaastra (1959), seem to indicate that the ratio photosynthesis/ 

 radiation in the range of light limitation is approximately the same for 



dry weight gm. 

 2iO- 



dry weight gm 

 240- 



X ° • 

 in * X 



O ~ X 



o .0 _ 

 = ' o* -I 



• •*• * 



200 iOO 600 800 1000 1200 UOO 



12 18 30 21. 29000 



4cal cm,' 



trtsti 

 2100 



weight gm. 



fresh weight gm. 



tqo 





• • 



•SPINACH 

 XLETTUCE 



1000 



o RADISH 

 4 ENDIUC 



1200 K.00 



Stemp 



24 28 000 



*col cm.' 



' BEANS 

 ' PEUt 



■» CARROTS 



» CAULIFLOWER 



Fig. 3. The effect of heat- and radiation-sum on dry- and fresh- weight yield per 

 container of various vegetables. The data obtained in autumn are underlined. 



various crops. This fact would favour the result that the dry-weight yield 

 of various crops are comparable with each other in accordance with the 

 total radiation received (Fig. 3). Calculations made on energy conversion 

 of radiation into dry weight seem to indicate that various crops show nearly 

 the same conversion values (Wassink, 1948). Further experimental details 

 and discussions concerning heat sum, total radiation and its practical 

 application have been given elsewhere (Bierhuizen, i960). 



