48 Bulletin 393 



Fletcher (iqoo), (loff (igoi), Green (1902), Close (i 90,^5 ), Lewis and 

 Vincent (1909), Bellair (1910), and Gardner (1913) — -recognize, as does 

 Waite, that there are other factors, aside from self-sterility, which cause 

 the falling of blossoms and immature fruits, all of them seem inclined to 

 attach special importance to the necessity of cross-pollination for many 

 varieties of fruits. It is pointed out that the structure of the flowers in 

 many cases is such as to inhibit self-pollination, whereas many flowers 

 have special modifications that seem to favor cross-pollination. The in- 

 fluence of such factors as weather, and the like, which favor or prevent 

 cross-pollination, are emphasized. 



Other workers, the chief among these being Miiller-Thurgau (1898, 

 1908) and Ewert (1906, 1907, 1910), while not ignoring the question of 

 pollination, have directed special attention to the importance of nutrition 

 as a factor in fruit setting. 



Miiller-Thurgau has done most of his work with the grape. He finds 

 (1898) that certain varieties can develop fruits without having the flowers 

 fertilized. If, however, the blossoms of such varieties are emasculated 

 and cross-pollination is prevented by inclosing the flowers in sacks, fruits 

 do not develop. This author holds that the entrance of the pollen tube 

 into the pistil may exert sufficient stimulus to initiate fruit development, 

 even tho fertilization does not occur. The stimulus is believed to be one 

 of a chemical nature which exerts an influence similar to that exerted 

 by fertilization, tho less far-reaching. This influence is not confined to 

 the single berry that has been pollinated or fertilized, but other berries 

 on the same bunch are affected in such a way that they may develop 

 even without the entrance of a pollen tube. 



Girdling the cane eight days before the flowers opened prevented the 

 shedding of berries, while similar canes not treated lost their immature 

 fruit. The berries produced were seedless, hence fertilization had not 

 occurred. Miiller-Thurgau believes that the ringing afforded better con- 

 ditions of nourishment for the flowers, so that the pollen tube could 

 germinate and enter the stigma and style. In a subsequent paper (1908) 

 this author records cases in which he obtained a set of seedless grapes 

 even without the stimulus of pollination. 



Miiller-Thurgau noticed also that the berries on that part of the vine 



above the girdle were heavier than those borne below the girdle. The 



latter usually contained some seeds while the former were often seedless. 



Berries on vigorous shoots were larger than those on relatively weak 



growth even tho the weak canes were girdled. On a given cane, the berries 



with seeds were larger than those without seeds, and, furthermore, the 



size of the faiit was found to be i)ro])()rtional to the number of seeds con^ 



tained in it. 



162 



