166 ORaANIC METAMORPHOSIS OF LEAVES 



The function of the stamens and pistils'-is purely repro- 

 ductive. At first the anthers are unruptured, moist, and 

 closed ; but, as they approach maturity, they become dry, 

 open their cells, and discharge their pollert on the stigmatic 

 surface of the pistil, which, about this time, becomes be- 

 dewed with a clammy fluid, which serves to retain the pol- 

 len. The grains of pollen absorb the moisture of the stigma 

 and emit delicate tubes, which penetrate the loose cellular 

 tissue of the style, and act as a conduit of the fecundating 

 matter of the pollen grains to the ovules, which these tubes 

 finally enter by means of their micropyle (Greek [j-ixpoq^ 

 little, and T,ukrj^ gate). The ovules, having received the im- 

 pregnating matter, the embryos, or miniature plants, begin 

 to form in them, and are gradually transformed into seed. 



The sap is now drawn to the forming fruit, a\^ay from 

 the petals and stamens, which fade and fall ojBF, having 

 fulfilled their important but ephemeral functions. The 

 stigmas and styles of the pistils being now useless to the 

 plant, disappear equally with the other parts. The ovaries 

 alone remain to aid in the ripening of the 'seed contained 

 within their cavities. 



The sap elaborated in the ordinary green leaves of the 

 stem, passes through the peduncle, or what was formerly 

 the flower-stalk, into the fleshy tube of the calyx, by which 

 it is retained, and which now gradually enlarges and con- 

 tinues to increase in size as long as the sap continues to 

 enter it. The gorged and swollen cellular tissue or sub- 

 stance of the apple is formed from this sap about the 

 cartilaginous walls of the ovaries. The surface of the 

 apple, whilst green, acts like an ordinary green stem-leaf 

 on the atmosphere, absorbing carbonic acid gas, and giving 

 out oxygen. As it slowly loses its green color, and assumes 

 a ripe and ruddy appearance, it ceases to do this, absorbing 

 the oxygen instead of giving it out. At maturity the stalk 

 ceases to afford any further passage for the fluids, and be- 

 comes finally unequal to the task of supporting the fruit; 

 so that it falls to the ground. Here it lies, unless eaten by 

 cattle, till it decays. On the approach of Spring, the seeds 



