Experiments on Plants 785 



C. A vacuum is made, then oxygen is admitted until normal 

 pressure has been restored; then the same operation was repeated; 

 finally this superoxygenated atmosphere (the sample of which in- 

 tended for analysis was unfortunately lost) is brought to a pressure 

 of 16 cm. 



October 12, a few seeds begin to germinate in A. 



October 14, germination begins in C. 



October 16, the sprouts are a little finer in A than in C. 



October 19, a few sprouts appear in B; A is still a little ahead 

 of C. 



October 23, in A, the barley is 8 cm. high, the cress 3 cm.; in C, 

 the barley is 7 cm. high, the cress 3 cm., but its sprouts are not quite 

 so fine as in A; B has only one barley sprout 6 cm. high at most, and 

 the cress is only 1.5 cm. high. 



Experiment CCCLIV. November 4. Sowing of barley and cress 

 on wet paper (a score of seeds). 



A. Air at normal pressure. 



B. Air at a pressure of 15 cm. 



C. 71% of oxygen, brought to a pressure of 20 cm., which cor- 

 responds to 18% at normal pressure. 



November 7, a few sprouts appear in A. 

 November 8, a few in C. 



November 11, beginning of germination in B. 

 November 25, conditions are as follows: 



A. The seeds have all sprouted, the sprouts are very green; the 

 cress is about 2 cm. high, the barley 12 cm. 



B. Has risen to 25 cm. pressure. Cress longer, but not so green 

 as in A. Only 3 sprouts of barley, as long as, but thinner and less 

 green than in A. 



C. Has risen to 40 cm. pressure (consequently is less oxygenated). 

 The sprouts, very numerous and very fine, are quite like those in A. 



These experiments bring us to the same conclusions as the pre- 

 ceding ones. We see, in fact, that seeds sown in superoxygenated 

 atmospheres have sprouted as quickly as in air at normal pressure, 

 in spite of the low barometric pressure to which they were sub- 

 jected. The low pressure therefore has no effect when the percent- 

 age of oxygen is sufficient to maintain the real tension of this gas 

 at a value approximating that in ordinary air at 76 cm. 



It is proved then that the delay in germination noted in all the 

 preceding experiments when the barometric pressure is very low 

 is due to low oxygen tension. The seeds do not absorb enough, even 

 though they have at their disposal very great quantities of oxygen 

 in weight. As in the case of blood corpuscles, absorption of oxygen 

 by plant cells is in proportion to the outer tension of this gas. 



It was interesting to find out the lower limit of pressure at 

 which germination can take place. The preceding experiments 



