ATMOSPHERIC AIR AS THE FOOD OF PLANTS. 23 
tion, viz: in germination. We know that the presence of 
oxygen is an indispensable requisite to the sprouting seed, 
and is possibly the means of provoking to action the dor- 
mant life of the germ. The ingenious experiments of Traube 
(H. C. G., p. 326.) demonstrate conclusively that free 
oxygen is an essential condition of the growth of the 
seedling plant, and must have access to the plumule, and 
especially to the parts that are in the act of elongation. — 
De Saussure long ago showed that oxygen is needful to 
the development of the buds of maturer plants. He ex- 
perimented in the following manner: Several woody twigs 
(of willow, oak, apple, etc.) cut = 
in spring-time just before the 
buds should unfold were placed 
under a bell-glass containing 
common air, as in fig. 1. Their 
cut extremities stood in water 
held in a small vessel, while the 
air of the bell was separated 
from the external atmosphere by 
the mercury contained in the 
large basin. Thus situated, the 
buds opened as in the free air, 
and oxygen gas was found to be 
consumed in considerable quan- Fig. 1. 
tity. When, however, the twigs were confined in an 
atmosphere of nitrogen or hydrogen, they decayed, with- 
out giving any signs of vegetation. (Hecherches sur la 
Vegetation, p. 115.) 
The same acute investigator found that oxygen is ab- 
sorbed by the roots of plants. Fig. 2 shows the arrange- 
ment by which he examined the effect of different gases 
on these organs. A young horse-chestnut plant, carefully 
lifted from the soil so as not to injure its roots, had the 
latter passed through the neck of a bell-glass, and the stem 
was then cemented airtight into the opening. The bell 
