352 
PHYSIOLOGY. 
BOOK II. 
soon after beginning to swell, from want of an accumulation 
of food for its support ; while, if the same plant is not 
allowed to bear fruit until it has provided a considerable 
supply of food, as will be the case after the leaves are fully 
formed, and have been some little time in action, the fruit 
which may then set swells rapidly, and speedily arrives at 
the highest degree of perfection of which it may be sus- 
ceptible. And in woody trees, also, a similar phenomenon 
is observable : it is well known to gardeners, that, if a season 
occurs in which trees in a state of maturity are prevented 
bearing their usual crops, the succeeding year their fruit is 
unusually fine and abundant ; owing to their having a 
whole year’s extra stock of accumulated sap to feed upon. 
The cause of the fruit attracting food from surrounding 
parts is probably to be sought in the phenomenon called 
endosmose. All the sap that may be at first impelled into 
the fruit by the action of vegetation, not being able to find 
an exit, collects within the fruit, and, in consequence of 
evaporation, becomes gradually more dense than that in the 
surrounding tissue-: it will then begin to attract to itself 
all the more aqueous fluid that is in communication with it ; 
and the impulse, once given in this way to the concentration 
of the sap in particular points, will continue until the growth 
of the fruit is completed, and its tissue so much gorged as to 
be incapable of receiving any more food, when it usually 
falls off 
No one has studied the effects of fruit upon the atmosphere, 
and the nature of the chemical changes it undergoes, with 
more success than Theodore de Saussure and Berard, an 
account of whose discoveries I partly translate and partly 
condense from De Candolle. According to the first of these 
original observers, “ Fruits, while green, whether leafy or 
fleshy, act much as leaves either in the sun or in shade, and 
differ from those organs principally in the intensity of their 
action. In the night they destroy the oxygen of their atmos- 
phere, and replace it with carbonic acid, which they partially 
absorb again. This absorption is generally less in the open 
air than under a receiver : and, their volume remaining the 
same, they consume more oxygen in darkness when distant 
