67 



top for taking up the blocks of ice during the night. Between the two 

 chambers is placed the cooling cell which causes the required cold in the 

 cupboard. 



The system described above has satisfied us that it is relatively simple 

 to keep the temperature constant at about 10° Centigrade, and that great 

 temperature fluctuations cannot take place. 



Now we come to the discussion of the second principal group, that of 

 the thoroughly ripe seeds. According to their reaction when germinating 

 at a reduced temperature they can be divided into two sub -sections :— 



Firstly, seeds germinating better when subjected to an alternating, 

 temperature than to a constantly low one. 



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Secondly, seeds requiring a constant low temperature. 



Consulting the existing literature, we generally find suggested an 

 alternation between 20° and 30° Centigrade. This is likewise used for many 

 seeds at Wagehingeh because it really seems to us the best method for their 

 germinating, for instance for the. seeds of Anethum graveblens, Agrostis 

 stolonifera, Brassica oleracea and Rapa, Carum Carvi, Festuca pratensis, 

 Phleum pratense, Raphanus sativus and other kinds. For 18 hours a 

 temperature of 20° C. is maintained, which is raised during the remaining six. 



It appeared, however, to us, that instead of an upward alternation, 

 a lower one is advantageous for various seeds, and that this alternation 

 yields the best results when using Jacobsen's method. Consequently our 

 method, " Copenhagen alternating," came into use with us, in which the 

 seeds are brought to, and kept for four hours at, the temperature bf 25-28°C. , 

 by heating the apparatus, after which the warm water at 32° C. is quickly 

 substituted by cold water, from the main tap, at 11-14° C. According to 

 Dorph Petersen's (55) description, an alternating temperature of 18-26° C. 

 on the Jacobsen's incubator is also used at Copenhagen. Moreover, I will 



C 2 



