782 Experiments 



shade of green; but at the end of two weeks, there were the follow- 

 ing differences in the two bells. 



In rarefied air the shoots had reached the height of 6 inches, and 

 in the compressed air 9 to 10 inches. The former were unfolded and 

 soft; the latter were rolled around the stem and were firm. Finally, 

 the former were moistened on the surface, and especially towards the 

 tip, with drops of water, two of which were always opposite each 

 other, whereas the latter were almost dry, especially on the surface. 

 This difference surprised me and my classes; I am inclined to believe 

 that the decrease in the height of plants, as one ascends mountains, 

 is the result rather of decreased pressure than of decreased tempera- 

 ture. 



We see that really no conclusion can be drawn from this at- 

 tempt, since the point of comparison, the control, that is, germina- 

 tion under normal pressure, had been forgotten; a derogation of the 

 rules of the experimental method which is unfortunately too com- 

 mon in naturalists. 



Subchapter I 

 PRESSURES LOWER THAN ONE ATMOSPHERE 



1. Germination. 



Let us begin with experiments made at pressures less than that 

 of the atmosphere, and first, by experiments on germination. 



Experiment CCCXLIX. May 21. Wheat. Sown on damp earth, in 

 about equal numbers of seeds and covered by bell-jars. 



A. Bell of 2.2 liters. Left at normal pressure. 



B. Bell of 7.1 liters. Taken to 50 cm. pressure. 



C. Bell of 11 liters. Taken to 25 cm. pressure. 



May 11. A. The shoots are about 20 cm. high; they are very fine, 

 very green, very numerous. 



B. The shoots are not more than 15 cm. high; they are much less 

 numerous, but quite green and erect, although rather sickly in ap- 

 pearance. 



C. Not more than 10 cm.; shoots scanty, yellow, drooping. 

 May 27. A: all up and growing green and thick-set. 



B : germination much less advanced. 

 C: Much less yet. 



Several times during the experiment there was a leak and a 



vacuum had to be restored; the air therefore was sufficiently renewed. 



The earth was well watered and the air saturated with moisture. 



Experiment CCCL. June 17. Barley. 



Sown in pots full of earth, in equal number of seeds, and placed 

 immediately: 



A. Under a bell of 2.2 liters. Left at normal pressure. 



B. Under a bell of 7.1 liters. Taken to 50 cm. pressure. 



C. Under a bell of 11 liters. Taken to 25 cm. pressure. 



