212 
always decomposed, which has been proved by the 
experiments of M. Sennebier. 
When the fluid taken up by the roots of plants 
contains much carbonaceous matter, it is probable 
that plants may give off carbonic acid from their 
leaves even in the sunshine. In short, the func- 
tion of the leaf must vary according to the com- 
position of the sap passing through it, and according 
to the nature of the products which are formed 
from it. When sugar is to be produced, as in early 
spring at the time of the developement of buds 
and flowers, it is probable that less oxygene will be 
given off, than at the time of the ripening of the 
seed, when starch, or gums, or oils, are formed ; 
and the process of ripening the seed usually takes 
place when the agency of the solar light is most 
intense. When the acid juices of fruits become 
saccharine in the natural process of vegetation, 
more oxygene, there is every reason to believe, 
must be given off, or newly combined, than at other 
times ; for, as it was shown in the Third Lecture, 
all the vegetable acids contain more oxygene than 
sugar. It appears probable, that in some cases, in 
which oily and resinous bodies are formed in vege- 
tation, water may be decomposed ; its oxygene set 
free, and its hydrogene absorbed. 
Mr. Berard, of Montpellier, has shown that fruits 
in ripening convert the oxygene of the air into 
carbonic acid; and that the process of ripening 
may be suspended by the exclusion of the fruit 
from oxygene gas, and that it will go on again after 
a certain interval of time. Unripe peaches, plums, 
