FUNCTION.] ITS EFFECTS ON THE ATMOSPHERE. 253 



third leaf, it rarely sets or arrives at maturity, but falls off 

 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 susceptible. 

 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. 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 evapo- 

 ration, becomes gradually more dense than that in the sur- 

 rounding 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 atmo- 

 sphere, 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 



