786 Experiments 



show already that it still takes place, though very slowly, at the 

 pressure of 15 cm., a pressure much lower than that of the atmos- 

 phere at the summit of the highest mountain, Mount Everest in the 

 Himalayas. 



The following experiments answer this question. 



Experiment CCCLV. December 14. Barley (about a dozen seeds) 

 and cress on wet paper. Bells of 1.5 liters. 



A. Air; normal pressure. 



B. Air; pressure of 6 cm.; the oxygen tension corresponds to 

 76 : 6 = 21 : x = 1.6% at normal pressure. 



December 17. A. A few seeds of cress have split their coverings. 



December 20. A. All the seeds of cress have split their cover- 

 ings; a few seeds of barley have sent out radicles. 



B. Pressure of 7 cm.; nothing has appeared. 



January 14. A. The cress seeds have germinated; the barley 

 shoots are 12 cm. high. 



B. Two barley seeds have sprouted; they are 6 cm. high. All 

 the seeds of B, both cress and barley, sprout when brought to nor- 

 mal pressure. 



Experiment CCCLV I. March 11. 40 seeds of barley and cress sown 

 on wet filter paper. 



A. At normal pressure. 



B. In a bell of 7 liters, brought to a pressure of 4 cm. 



March 28. A. All sprouted; the barley has sprouts 4, 5, and 6 cm. 

 high; B, in which the air was changed March 15, 18, 23 and 26, shows 

 no sign of germination. Pressure is raised to 8 cm. 



April 26. The air in B was changed March 31, and April 6, 8, 

 and 11; nothing has appeared yet except molds. 



Sown in the air on wet paper. 



May 20. Fine shoots of cress, but the barley has not sprouted. 



It is therefore at a pressure of about 7 cm. that germination can 

 no longer take place. It is interesting to note that this decom- 

 pression is exactly that at which warm-blooded animals succumb 

 rapidly, no matter what precautions are taken, and at which cold- 

 blooded vertebrates cannot live long. 



If we look for the percentage of oxygen to which the oxygen 

 tension at this pressure of 7 cm. corresponds at normal pressure, we 

 find it by means of the following proportion 20.9: 7 = 76: x = 2.5. 

 This is very close to the experiments of Lefebure, who showed that 

 germination of the turnip still takes place, although slowly and in- 

 completely, when the air contains only 1/32 of oxygen, that is, 

 3.4%. 



