the addition of carbonic acid furnished by the roots 9 
while the atmospheric air was diminished from the 
attraction of the carbonic acid, either by the 
roots themselves, or by the water. From these 
experiments, and from other considerations, M. 
de Saussure concludes, that the contact of oxygen, 
gas with the roots of plants is useful to vegeta- 
tion *. 
278. Lastly, M. de Saussure confined the woody 
stems of plants, immediately before the appearance of 
their buds, in vessels of common air, with sufficient 
water to carry on their growth, and they came into 
leaf like those in the open air ; but in nitrogen and 
hydrogen gases they were unable to make this deve- 
lopment, and perished without exhibiting any sign, 
of vegetation. When deprived of their leaves, the 
ligneous stems of plants vitiate common air, either in 
sunshine or in the shade, without changing its vo- 
lume ; and replace, with an equal bulk of carbonic 
acid, the oxygen gas which they make tft disappear. 
The stems of the willow, the oak, the poplar, the ap- 
ple and the pear, were employed in these experi- 
ments. 
279. These effects which the flowers, the fruits, 
the roots, and the stems of plants produce in the air, 
at all times, and in all situations, accord completely 
with those which the leaves and other green parts of 
vegetables produce in the shade, since they all, more 
or less, convert the oxygenous portion of the air into 
an equal bulk of carbonic acid. These facts afford, 
* Recherches, p, 104, 106. 
