Experiments on Plants 791 



Experiment CCCLXX. June 19. Barley and cress on wet paper. 



A. Under a bell; normal pressure. 



B. 6 atmospheres of air. 

 Air changed every day. 



June 22. A. Cress germinated; little stalks of barley started. 



B. Cress hardly shows any sign; a few barley radicles to be seen. 



June 29. A. Cress, 3 cm., very green and smelling strong; barley 

 from 12 to 20 cm. 



B. Cress, 2 cm., very green and smelling strong; barley, stalks 

 1.5 cm. high. 



Experiment CCCLXXI. August 17. Sowings on wet paper of 

 seeds of marvel-of-Peru, castor beans, and melon, which were 

 decorticated after being kept for two days in water. 

 A. Cylindrical apparatus at 2 atmospheres of air. 



B. Open vessel. 



August 18. 9 o'clock in the morning; in A and in B, some mar- 

 vels-of-Peru have germinated. 



I raise A to 6 atmospheres, and change the air every day. 



August 23. A. Same condition. 



B. The radicles of the melon and castor bean seeds are appear- 

 ing. 



August 26. A. Nothing has sprouted. 



B. The marvels-of-Peru are 2 to 3 cm. high; the melon and cas- 

 tor bean seeds have sent out all their roots. 



B continues to sprout in the open air, whereas nothing sprouts 

 in A. 



These experiments show very clearly that, beginning with a cer- 

 tain pressure, germination is delayed, and that at a higher pressure 

 it does not take place. Furthermore, certain seeds die then and 

 cannot develop when brought back to normal pressure. 



But before studying these results in detail, we must once more 

 settle the question which we have encountered several times, and 

 find out whether this fatal effect is due to the pressure itself or to 

 the increased chemical tension of the oxygen. 



And here, once more we have the different methods which we 

 are accustomed to using: 1). to make the compression with air with 

 low oxygen content, so that the tension of this gas is equivalent to 

 that of the oxygen in the air at normal pressure; 2). to make ex- 

 periments at normal pressure with air which has a greater oxygen 

 content than ordinary air; 3). to use both low pressure and air 

 which is superoxygenated, so that we obtain high tension with 

 low pressure. 



