F. KiDD AND C. West 243 



to eliminate such exosmosis as far as possible by using the niininuun 

 amount of water necessary for the complete swelling of the seed. 



That the exosmosis of soluble food-material, or the lack of oxygen 

 combined with accumulation of carbon dioxide which must necessarily 

 accompany the immersion of the seed in water, may become sufficiently 

 pronounced to cause very definite injury, resulting in a fall in germination 

 percentage and a decrease in the subsequent yield, is clear from the 

 work of numerous authors, and it is in this connection in particular 

 that the conditions under which the soaking treatment is carried out 

 are important. For example, if the seeds are immersed in a dense mass, 

 even with a minimum amount of water, the lack of oxygen and accumu- 

 lation of carbon dioxide resulting at normal temperatures from such 

 conditions may in a very short time cause seiious injury to the seeds, 

 as the present authors have found. Again, it has been shown that in 

 the case of some seeds {e.g. peas and beans) pronounced injury results 

 even after very short periods of soaking when excess of water is used, 

 probably for the same reason (cf. Kidd and West(2i)). 



If the temperature is high {e.g. 25° — 30° C.) the injurious effects are 

 more diflficult to avoid; on the other hand, for some as yet unexplained 

 reason, low temperatures (0°-10° C.) appear in many cases to exert a 

 specific injurious action upon seeds soaking in water (cf. Kidd and 

 West (22)). 



In any case too long a period of soaking produces injury and death. 

 Coupin(5) has shown that whereas some seeds can withstand only a brief 

 period of immersion in water, others can withstand a long one. 



The results of experiments in which stagnant water is compared with 

 running water in its effect upon submerged seeds, indicate that lack of 

 oxygen and accumulation of carbon dioxide, rather than the loss of soluble 

 substances, are chiefly responsible for the injurious effects observed. In 

 running water as compared with stagnant water, although a greater 

 exosmosis of soluble matter occurs, the oxygen supply to the seed is 

 maintained and carbon dioxide accumulation is reduced to a minimum. 

 Under these conditions certain seeds can germinate and form roots and 

 leaves (cf. Jodin(20)). In stagnant water, on the other hand, even when 

 leaching is reduced to a minimum, germination is inhibited and injury 

 and death eventually follow. 



