765. How the fruit GROWS. In its earliest stages the pericarp consisted of a structure similar to that of green leaves, composed of parenchyma, pleurenchyma, vessels, and epidermis with stomata. Its distended growth afterwards results from the accumulation of the flowing sap, which here finds an axis incapable of extension. Thus arrested in its progress, it gorges the pistil and adjacent parts, is condensed 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 starch 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 organs which have no chlorophylle 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 poller 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 (C12 H10 O10) contains proportionably more carbon than sugar (C12 H12 O12) contains. It is probable that these two phenomena in vegetation are always co-existent