FERTILIZATION. 179 



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, acidi- 

 fying the juices. 



441. In the same way we account for the produc- 

 tion of honey in the flower. Copious deposits of starch 

 are provided in the receptacle and disk ( 85). At the 

 opening of the flower, this is changed to sugar, to aid 

 in the rapid development of those delicate organs 

 which have no chlorophyl wherewith to assimilate 

 their own food. The excess of sugar flows over in the 

 form of honey. 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 ! 



442. Experiment has proved that in all these cases of the formation of 

 sugar from starch, a molecule of water is absorbed a process which we might 

 expect, since starch (C ia H 20 Oi ), or n(C 8 H 10 O 5 ) contains proportionably two 

 less hydrogen and one less oxygen than sugar (d 2 H 22 On) contains. 



443. Pollination, cross-fertilization, etc. Pollen is 

 essential to the fertilization of the flower. It must 

 not only be produced, but must also in some way be 

 conveyed to the stigma, and lodged on its surface. 

 Another requisite is that the pollen and pistil shall 

 either be : 1st, parts of the same flower ; or, 2d, of other 

 flowers of the same plant ; or, 3d, of the same species ; 

 or, 4th, of closely related species. In the first and 

 second cases the -process may be called self-fertiliza- 

 tion ; in the third case, cross-fertilization; in the 

 fourth case, hybridization. 



444. Whether the first, second, or third process 

 shall prevail in any given species will depend on the 



