381] B. E. Livingston and E. E. Free 183 
the response of the root-system to deficiency of oxygen in 
the soil atmosphere varies widely in different kinds of plants. 
Some species are injured by a very slight deficiency below 
the oxygen content of the general atmosphere. A swamp 
willow, probably Salix nigra, endures successfully the com- 
plete, or almost complete, exclusion of oxygen from its roots. 
In the case of those plants which are injured by deficient 
soil oxygen it is interesting physiologically that the first 
effect of oxygen deprivation is an interference with the ab- 
sorption of water by the roots. In the experiments the 
apparatus for the supply of water is so arranged that the 
amount of water taken up by the soil from the porous cups 
of the auto-irrigator can be measured for periods as short 
as one hour. The amount of water thus taken up depends 
in part on the temperature. The surface tension of the 
water films in the soil varies with temperature and this con- 
trols the amount of water held in the water-film system. 
However, this error disappears for periods the initial and 
final temperatures of which are nearly the same (for in- 
stance, the usual 24-hour period) and a correction can be 
made for the error in the case of shorter periods or other. 
periods which do not satisfy this condition. When the tem- 
perature error is thus eliminated, the absorption of water 
from the auto-irrigator is closely parallel to the intake of 
water by the plant roots. With the plants that are sensi- 
tive to deficiency of oxygen in the soil air, it is found that 
the replacement of the normal soil atmosphere by nitrogen ° 
is followed within a few hours by nearly complete cessation 
of water-intake by the’ roots. With the most sensitive species 
tested, namely, Coleus blumei and Heliotropium peruvianum, 
this cessation of water-intake occurs always within 24 hours, 
usually within 12 hours, after the soil oxygen is removed. 
This time period varies with the individual plant, perhaps 
because of differences in the root-system but probably also 
because of differences in the completeness with which the 
soil oxygen originally present is replaced by the nitrogen. 
Since the oxygen must be displaced by washing out with 
