64 



15° to 20° Centigrade, and. continued for longer periods than for normal 

 seed." 



At Wageningen the best means for the germination of newly harvested 

 or newly threshed grains was a temperature of 10° C. during five days and 

 afterwards a higher one of 20° C. A large series of comparative tests was 

 made during the last three years and extraordinarily .favourable results 

 were obtained by the use of this method with poorly after-ripened wheat, 

 rye and oats. The following tables I, II and III, each consisting of ten 

 examples, will give an idea of this. Practically a delayed germination did 

 not occur in the case of the three above-mentioned kinds. With barley 

 samples, however, it was somewhat different. The results in most cases 

 were satisfactory (table IV), but oases occur in which the favourable 

 influence, while obvious, is not quite complete (table V). In such cases, 

 however, the highest figure for the germinative power could be reached 

 by an artificial after-ripening at a raised temperature. In the case of 

 barley, the success of the W^ method, as we call it at Wageningen, depends 

 apparentlj' on the degree of after-ripening ; some years there will be more 

 difficulties than in others. Last winter, for example, when delayed ger- 

 mination did not often occur, the Wjq method turned out absolutely 

 satisfactory for barley. 



Lettuce (Lactuca sativa) seeros to show an analogous phenomenon. 

 Considerably better results are often obtained with a low temperature than 

 with one of 20° C. In many other cases, however, the Wjj method yields 

 higher germination figures. 



Although I have not yet arrived at any definite conclusion, I believe 

 this difference of behaviour to be caused by different degrees of ripeness, 

 so that for insufficiently ripened lettuce-seeds the low temperatiu'e is 

 reconamended, but for the well-ripened ones the Wjo method is the best. 

 The figures in table VI, demonstrating the behavioiu* of some six samples 

 of seed not fully after-ripened, support this opinion. Probably a method 

 exposing the after-ripened seed to a regular temperature, alternating 

 between 10° C. and 20° C, will give better results than a constant one of 

 10° C. The data, which I have at my disposal at present are, however, not 

 sufficient to enable me to give a definite judgment on this question. 



The same is the case with corn salad (Valerianella olitoria) which, 

 being after-ripened, germinates well at an even temperature, but, until it is 

 after-ripened, prefers a low alternating germination temperature. 



