RESPIRATION AND OXYGEN. 33 



unglazed area 2 inches square was left on the opposite side; in others 

 the unglazed area was a zone; while in others all water was added 

 from the bottom. After 2 days the pots with unglazed areas for 

 the access of air were sealed by pouring the usual wax over the surface 

 of the soil. After a period varying from 3 to 5 days in the different 

 series, the soil-mass was carefully removed from the pots in such a 

 way as to preserve the relation to the unglazed area. In all cases 

 the bean seeds were found to have decayed without germinating and 

 sunflower alone was used in the remaining series. Even the sun- 

 flower failed to germinate in the soils constantly saturated from 

 below. The two pots with the unglazed square gave positive curva- 

 tures toward this area in all three series, though this was less true 

 of those with the unglazed zone, owing to the more general diffusion 

 of the air. In the former, all the seedlings showed right-angled 

 curvatures toward the direction of air access, without a single nega- 

 tive or opposite response. 



( 



AIR OF SOIL AND PLANTS. 

 AIR-CONTENT OF THE SOIL. 



Earlier researches. Boussingault and Lewy (1853 : 5) were the first 

 to determine the composition of the air contained in the soil. They 

 analyzed the air-content of various soils, namely, soil recently man- 

 ured, soil of a field of carrots, soil of a vineyard, forest soil, sandy 

 soil, humus soil, bed of asparagus, beet field, field of alfalfa, etc. 

 The highest amount of carbon dioxid, 3.83 per cent, was found in 

 the soil containing abundant humus, and conversely, the smallest 

 amount of oxygen, 16.43 per cent. Soil recently manured yielded 

 2.17 to 2.25 per cent of carbon dioxid, but after frequent rains this 

 had increased to 9.74 per cent and the oxygen had decreased to 

 10.35 per cent. Sand contained the smallest amount of C0 2 , 0.11 

 to 0.19 per cejit, and the largest amount of oxygen, over 20 per cent. 

 They found the average amount of C0 2 in soils not fertilized for a 

 year to be 22 times the amount in normal air, while in manured 

 soils the amount was 245 times greater. They concluded that the 

 greater part of the carbon dioxid is derived from the oxidation of 

 organic matter in the soil, and that a small but constant part of the 

 oxygen combines with the hydrogen derived from fermentation. 



Petenkoffer (1871 : 395) determined the amount of carbon dioxid 

 in the soil-air at Munich from September 1870 to November 1871. 

 Samples were taken at 0.66, 01.5, 2.5, 3, and 4 meters. He found 

 that the air of the upper soil-layers contained less carbon dioxid 

 from August to June, and more throughout June and July. At 1.5 

 meters the amount rose from 0.26 per cent in January to about 0.8 per 

 cent in July, and reached its maximum at about 1 per cent in August 

 to fall to 0.5 per cent in November. At 4 meters the amount rose 



