24 HOW CKOPS FEED. 
was placed in a basin of mercury, C, D, to shut off its con- 
tents from the external air. So much water was intro- 
duced as to reach the ends of the principal roots, and the 
space above was occupied by com- 
mon or some other kind of air. In 
one experiment carbonic acid, in a 
second nitrogen, in a third hydro- 
gen, and in three others common 
air, was employed. In the first the 
roots died in seven or eight days, 
in the sccond ang third they perish- 
ed in thirteen or fourteen days, 
while in the three others they re- 
mained healthy to the end of threc 
weeks, when the experiments were 
concluded, (Recherches, p. 104.) 
Flowers require oxygen for their 
development. Aquatic plants send 
their flower-buds above the water 
to blossom. De Saussure found 
Fig. 2. that flowers consume, in 24 hours, 
several or many times their bulk of oxygen gas. This 
absorption proceeds most energetically in the pistils and 
stamens. Flowers of very rapid growth experience in 
this process, a considerable rise of temperature. Garreau, 
observing the spadix of Arum italicum, which absorbed 
28} times its bulk of oxygen in one hour, found it 15° F. 
warmer than the surrounding air. In the ripening of 
fruits, oxygen is also absorbed in small quantity. 
The Function of Free Oxygen.—All those processes 
of growth to which free oxygen gas is a requisite appear 
to depend upon the transfer to the growing organ of mat- 
ters previously organized in some other part of the plant, 
and probably are not cases in which external inorganie 
bodies are built up into ingredients of the vegetable struc- 
ture. Young seedlings, buds, flowers, and ripening fruits, 
