784 ' Experiments 



when we were speaking of animals. Are the slowness and the 

 checking of germination due to the low pressure as a physical con- 

 dition, or should these phenomena be attributed to the lowered 

 oxygen tension of the air? All that I have said hitherto justified 

 me in maintaining the truth of the latter hypothesis. Nevertheless 

 I wished to test it again by double experimental control, although, 

 it is true, I limited myself to a small number of experiments. 



There are two methods to be used, as we have already seen. We 

 can study germinations at normal barometric pressure, but in 

 atmospheres with low oxygen content. Evidently, if in this case 

 we see that germination takes place more quickly in air than in a 

 medium with less oxygen, the lack of oxygen must be the cause. 



We can also compare with germinations in air, at normal pres- 

 sure, other germinations at low pressures but in superoxygenated 

 media, so that the real tension of the oxygen is about equal to that 

 in air under ordinary barometric conditions. 



Here first is an experiment made by the first of these methods. 



Experiment CCCLII. July 12. Barley sown on wet filter paper; 

 20 seeds in each plate. 



A. Bell of 13 liters; left in air at normal pressure. 



B. Bell of 20 liters; I make a vacuum, and admit air in which 

 the oxygen content has been made very low by burning phosphorus. 

 The mixture contains 10% of oxygen. 



It will be noted that the capacity of the bells varies inversely 

 with the quantity of oxygen. 



July 16. The sprouts in A are stronger than in B. 



July 18. The sprouts in A (air) are 12 cm. on the average; those 

 in B (nitrogen) 10 cm. 



July 22. A on the average 21 cm.; B on the average 19 cm. 



This experiment shows very clearly that in air with low oxygen 

 content, even if the total quantity is quite sufficient, germination 

 takes place less quickly than in ordinary air. 



I did not think I should dwell on this sort of experiments, be- 

 cause the former researches of Senebier, Saussure, Lefebure, etc., 

 although they lack precision from the point of view of chemical 

 analysis of the atmospheric medium, give clear testimony for the 

 same conclusion. 



Here are some experiments made by the second method. 



Experiment CCCLIII. October 9, 1872. Barley and cress, sown 

 on wet paper. 



A. Air at normal pressure. 



B. Air at a pressure of 16 cm. 



