27 t PHYSIOLOGICAL BOTANY. PART II. 



their fecula, oils, &c., and the proportion of carbon also 

 is then at a maximum. Hence it acquires an increased 

 power of resisting decomposition, and of preserving its 

 vitality under every temperature to which it is likely to 

 be naturally exposed. 



.Most ripe seeds are of greater specific gravity than 

 water, unless (as in the common Indian cress, Tropa-oliun 

 tntijna) air happens to be contained in their envelopes, 

 when they will float. 



('J7-.) Stimulant* to Maturation. An increase of 

 temperature materially accelerates the period in which 

 fruits ripen, and also improves their flavour. Advan- 

 tage is taken of this fact to wrap fruit in thin bags, to 

 place it under glass, or upon slates of a dark colour. 

 That elaboration of the juices by which the fruit is 

 ripened is a local operation, and takes place within the 

 fruit itself. This is clearly shown where a tree, whose 

 fruit possesses a peculiar flavour, has been grafted upon 

 the stock of another kind whose fruit possesses a very 

 different quality : no alteration is produced upon the 

 graft. Also where fruit has been gathered before it 

 was quite ripe it will nevertheless ripen, as every one is 

 aware is the case in apples, oranges, and many others. 



The process of ringing the branches or stems of fruit 

 trees, already alluded to in art. 190., considerably acce- 

 lerates, as well as secures the maturation of the fruit. 

 In the vineyards of France this has been practised on a 

 large scale, and a peculiar instrument invented for the 

 purpose ; and the results have shown that the operation 

 accelerates the ripening of the grapes from twelve to 

 fifteen days. De Candolle mentions a vine near Geneva 

 which regularly flowered every year, but had never pro- 

 duced fruit until this operation was performed upon it ; 

 and then the fruit set, and proved to be the small 

 Corinth grape, which in commerce is known under the 

 name of dried-currants or plums. 



(273.) Flavour of Fruit. We are wholly unac- 

 quainted with the physiological causes upon which the 

 different flavours of fruits depend. In the earlier state 



