RIPENING OF FRUITS. 151 



763. ^HB PROCESS. To this end water and oxygen are absorbed, tbe 

 gluten begins decomposition, forming yeast ; fermentation ensues ; lieat 

 is produced by the slow combustion of the carbon with oxygen form- 

 ing and evolving carbonic acid, by which process some of the oil and 

 starch is destroyed, while another portion gains water and turns toj 

 sugar. All this within the cells of the seed. 



RIPENING OF FRUITS. 



764. In the pericarps of most fleshy fruits (grape, pear, apple, peacL, 

 strawberry), sugar exists before germination, ready formed in the process 

 of ripening. 



765. How THE FRUIT GROWS. In its earliest stages the pericarp consisted of a 

 structure similar to that of green loaves, composed of parenchyma, pleureuchyma, 

 vessels, and epidermis with stomata. Its distended growth afterwards results from 

 the accumulation of the flowing sap, which here finds an axis incapable of exten- 

 sion. Thus arrested in its progress, it gorges the pistil and adjacent parts, is con- 

 densed by exhalation, assimilated by their green tissues, which still perform the 

 office of leaves. Cell-formation goes on rapidly within, and the excess of cellulose 

 is deposited in the cells as starch. Oxygen is usually absorbed in excess, acidifying 

 the juices. 



766. How IT RIPENS. After the fruit has attained its full growth, 

 the process of ripening commences, during which the pulp becomes 

 gradually sweetened and softened chiefly by the change of the staixh 

 into more or less of soluble sugar. 



767. Honey. In the same way we account for the production of 

 honey in the flower. Copious deposits of starch are provided in the 

 receptacle and disc (§ 446). At the opening of the flower, this is 

 changed to sugar to aid in the rapid development of those delicate or- 

 gans which have no chlorophyllc wherewith to assimilate their own 

 food. The excess of sugar flows over in the form of honey. 



768. The wise economy of the honey is seen in fertilization. For, 

 attracted by it, the insect enters the flower, rudely brushes the pollen 

 from the now open anthers, and inevitably lodges some of its thousand 

 grains upon the stigma ! 



■769. Experiment has proved that in all these cases of the formation of sugar 

 from starch oxygen is absorbed and carbonic acid evolved, — a process which we 

 might expect, since starch (Cm Hio Oio) contains proportionably more carbon than 

 sugar (CiiHijOu) contams. It is probable that these two phenomena in vegetation 

 are always co-exiatent 



