CHAPTER XXIX 



FACTORS MORE DIRECTLY CONCERNED IN THE DEVELOP- 

 MENT OF THE FRUIT 



The discussion thus far has been hmited mainly to a consideration of 

 the primary results of fertilization. From the grower's standpoint, how- 

 ever, the nature and extent of its indirect effects are often of equal or greater 

 importance. 



The immediate or primary result of fertilization is the initiation of the 

 series of changes in the mature embryo sac leading to the development 

 of the embryo and endosperm. The changes subsequently occurring 

 in the ovarian wall and oftentimes in attached tissues result in the setting 

 and development of the fruit. These are the indirect or secondary 

 effects of fertilization. 



Stunulating Effects of Pollen on Ovarian and Other Tissues. — Before 

 fertihzation takes place, the pollen often has an important influence on 

 the development of ovarian and other tissues connected with the fruit. 

 This effect is independent of the process of fertilization and may be exer- 

 cised though fertilization never occurs. For example, Wcllington^^^ 

 secured fruits of the Seckel pear by applying to its stigmas pollen of the 

 Yellow Transparent apple, and Millardet^^ obtained fruits of certain va- 

 rieties of the European grape by employing pollen oi A^npelopsishederacea. 

 Presumably in neither case could fertilization occur, though the pollen 

 tubes may have entered the embryo sacs. Tritm-ated pollen applied 

 to the stigmas of certain curcurbits has induced a partial development of 

 their fruits ^° and fully formed but seedless fruits of certain species 

 have been obtained by applying to their stigmas spores of Lycopodium^^ 

 In both of these cases fruit development must be attributed to the stimu- 

 lating influence of the pollen or spores. Goodspeed''^ reports that emas- 

 culated but unpoUinated flowers of the Thompson Seedless grape do not 

 set fruit; however, emasculated and pollinated flowers set freely, though 

 the resulting fruits are seedless because of embryo sac degeneration. 



Some of the most interesting, and perhaps among the most striking, 

 cases of response to the stimulus of pollination are found among the 

 orchids.^' In most species of this family the ovule is in a very rudimen- 

 tary stage of development at the time of pollination. In some of these 

 if pollination is not effected the ovules never reach the stage at which 

 fertilization can take place, but immediately after pollination the tissues 

 of the ovule proceed to complete their development and finally reach the 



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