74 AERATION AND AIR-CONTENT. 



Bert (1876 : 1493) observed that an increase of the air-pressure 

 to 4 or 5 atmospheres, or of the oxygen-content to 60 per cent, was 

 either without any influence upon germination or merely hastened 

 it. But when the oxygen rose to 80 or 90 per cent, or the air was 

 compressed beyond 5 atmospheres, the harmful effect of the increased 

 oxygen-pressure was quickly evident. Germination was delayed and 

 the growth of the plants was weaker than under normal conditions, 

 the greater the pressure the weaker being the plant. The germina- 

 tion of starchy seeds suffered much more from the increased pres- 

 sure than that of oily seeds, and the latter could stand a much 

 higher pressure without damage. As for respiration itself, a much 

 smaller volume of oxygen was absorbed at a pressure of 11 atmos- 

 pheres than under normal conditions. Under reduced air-pressure, 

 germination took place more slowly the lower the pressure. It 

 ceased between 4 and 10 cm. without the seeds dying. 



GigHoh (1879 : 477; 1895 : 544) found that seeds of wheat, 

 Cynara, Vicia, and Phaseolus kept their power to germinate longer 

 in CO2 than in ordinary air when they were dry, but that they were 

 killed very quickly in it when wet. Wet seeds kept in oxygen and 

 in carbon monoxide failed to germinate. Seeds of alfalfa that had 

 been kept in hydrogen for 16 years gave a germination of 56 per 

 cent, while those in carbon monoxid gave 84 per cent. 



Bernard (1883 : 200) noted that seeds of cress were not able to 

 germinate in a mixture of air with one-sixth volume of CO2. When 

 exposed afterward to air, germination took place in normal fashion. 



Van Tieghem and Bonnier (1882 : 25) found that peas left in 

 open air for 2 years gave 90 per cent of germination, while those in 

 restricted air gave but 45 per cent, and in carbon dioxid, none ger- 

 minated. For beans, the respective percentages were 98, 2, and 0. 

 Castor-beans gave similar results, while wheat and flax showed little 

 difference in open and in closed air, but all agreed in failing to ger- 

 minate in CO2. 



Linossier (1889 : 820) concluded that amounts of CO2 up to 19 

 per cent delayed germination, and above this the number of germi- 

 nating seeds decreased with increasing content, but that germina- 

 tion was entirely suppressed only at higher percentages. Lettuce 

 seeds still germinated at 36 per cent, though cress seeds would not. 

 Carbon dioxid was considered to be a poison to which seeds were 

 variously susceptible. 



Lukas (1886 : 298) found that a varying air-pressure from 22 to 

 72 mm. was sufficient for the germination of seeds of Avena saliva, 

 Triticum vulgare, Panicum miliaceum, and Cucurhita pepo, but not 

 sufficient for the further development of the young seedling, or for 

 the germination of Brassica rapa, Lactuca saliva, etc. Atmospheric 

 air under a pressure of 70 to 168 mm. was sufficient for the growth 



