788 Experiments 



It is quite certain then that under the influence of low baro- 

 metric pressures, sensitive plants quickly lose their sensitivity and 

 die. Now we should learn the cause of this death. Should we 

 attribute it, as we have been accustomed, so to speak, to do hitherto, 

 to low oxygen tension? Should we merely blame the expansion of 

 the gases within the plant, an expansion which is due to the de- 

 compression and which would be great enough to affect such a deli- 

 cate plant fatally? 



The following experiment answers this question. 



Experiment CCCLX. July 25. Two pots, each containing 3 young 

 sensitive plants. 



A. Taken to a pressure of 25 cm. 



B. Pressure lowered 50 cm., and oxygen admitted then pressure 

 brought to 25 cm. The oxygen tension in this bell corresponds about 

 to that of the air at normal pressure. 



July 26. A. Sick. 



July 27. A. Dead; B. In good health. 



Here again the too low oxygen tension killed the sensitive 

 plants subjected to low pressure. 



Finally here is an experiment which, although it was made on 

 an almost microscopic plant, has a certain interest. 



Experiment CCCLXI. April 8. Fragments of frog eggs, with a 

 little of Priestley's "green matter." 



A. Flask at normal pressure. 



B. Flask at a pressure of 25 cm. 



April 25. Green matter abundant in A; nothing in B. 



So a lowering of the pressure is harmful to vegetation as it is 

 to germination; it kills plants at the same degree at which it kills 

 cold-blooded animals, and completely checks the life of seeds, with- 

 out, however, killing them entirely. 



The unity of the phenomena of respiration in the two kingdoms 

 is emphasized here very clearly. 



Subchapter II 

 PRESSURES ABOVE ONE ATMOSPHERE 



1. Germination. 



Let us now take up experiments made under increased pressure; 

 and first, germination. I have always made my sowings on wet 

 paper, because previous experiments have shown me that the pres- 

 ence of earth complicates the results. 



