78 AERATION AND AIR-CONTENT. 



due to increased mechanical pressure of the seed-coats or to their de- 

 creased permeability to gases, but to a stable condition of the embryo 

 slowly established during the period of inhibition by carbon dioxid. 

 This is contrary to the results of Crocker on Xanthium (1916), Shull 

 on Xanthium (1911), and Rose on Datura and Martynia (1915), all 

 of whom ascribed the effect to the low permeability of the testa to 

 oxygen, and a similar conclusion is indicated by Atwood for Avena 

 fatua (1914). 



Summary. Since germination is essentially a matter of respiration 

 and growth, it shows much the same response to anaerobic condi- 

 tions. The earliest investigators found that it was poor or alto- 

 gether absent in a vacuum, and similar results were obtained when 

 the oxygen was removed by other means. Hollo and Lefebure ob- 

 served that seeds would not germinate in pure nitrogen or hydrogen, 

 while Huber and Senebier stated that peas would do so, but lettuce 

 would not. They were unable to germinate most seeds in hydrogen, 

 in agreement with the results of Ingenhousz and Saussure, who ob- 

 tained no germination in it. The experiments of Huber and Senebier, 

 Saussure, Deherain, Ewart, and Maz6 have shown that seeds germi- 

 nate but poorly or not at all under water, especially when this is deep 

 and quiet. Rice germinates more readily under water than the seeds 

 of mesophytes, but the growth of the seedling seems to be inhibited 

 sooner or later. Reduction in the amount of oxygen or its pressure 

 beyond a certain point regularly delays or decreases germination. 

 Lefebure found that it took place normally in one-eighth or one- 

 sixteenth oxygen, but failed for the most part in one thirty-second. 

 Huber, however, was able to germinate lettuce seed only when the 

 oxygen reached a sixth. Dobereiner germinated barley at half the 

 normal air-pressure, and Bert, Lukas, and Schaible showed that con- 

 siderable reductions in pressure retarded germination more or less in 

 proportion. 



Contrary to the opinion of Humboldt and Rollo that seeds germi- 

 nate more readily in pure oxygen, most investigators have found that 

 the latter delays germination. Bohm noted that wet seeds in pure 

 oxygen stopped their development in the first stage, and Deherain 

 and Landrin observed that germination was less rapid than in at- 

 mospheric air, while Huber and Senebier had long before shown that 

 it was better in a mixture of 3 parts of hydrogen or nitrogen and 1 of 

 oxygen than when the amounts were reversed. In Bert's experi- 

 ments, an air-pressure of 4 to 5 atmospheres or an oxygen content of 

 60 per cent affected germination little or not at all, but above this 

 it was more or less delayed. 



Small amounts of carbon dioxid usually delay germination and 

 higher percentages inhibit it. Saussure stated that a small amount 

 retarded germination, and Bohm found that 5 per cent was sufficient 



