MICHIGAN ACADEMY OF SCIENCE. 
53 
chiefly muscular contraction and other processes which enlarge or re¬ 
duce the aerating cavity. In plants there is no such action. 
An actual problem illustrates, probably, more vividly than any dis¬ 
cussion, the enormous amount of air used by plants in the process of 
transpiration alone: At a temperature of 82° F., an oak requires 
1,111,111 cub. ft. of air per day to carry off the water of transpiration; 
a sunflower requires 1,500 cub. ft. per day; and one acre of cabbage re¬ 
quires 25,024,000 cub. ft. per day. These figures are calculated from the 
actual amount of water transpired and from the amount of Avater vapor 
held in suspension in the air at a given temperature. At a temperature 
of 72° it would, of course, require more, and at 92°- less, providing we 
assume that the plant transpires as freely at these temperatures, which 
is obviously an assumption which does not hold in nature, but, at the 
same time, serves the purpose of illustration. At the temperature 72°, 
82°, 92°, with the assumption just stated, the amount of air would be in 
the proportions, 32, 23, 16. 
Agricultural College. 
