Abscission of Flowers and Fruits of the Apple 49 



Vines growing in the open but protected from cold rains lost their fruit, 

 as did plants exposed to the rain. Miiller-Thurgau states that rain during 

 warm weather at blooming time does not necessarily have a detrimental 

 effect on subsequent fruiting. He is of the opinion that the falling of 

 blossoms and immature berries of the grape is due to an inadequate sup- 

 ply of easily respirable food. Pollination may overcome a temporary 

 shortage by affording a stimulating influence; fertilization is even more 

 effective in causing the set on weak vines or during unfavorable condi- 

 tions for assimilation and translocation of food. The conditions that 

 obtain for the grape are said to hold for the apple and the pear as well. 



Ewert (1906, 1907, 1909) has given considerable attention to the 

 development of seedless fruits. He believes that the development of 

 such parthenocari^ic fruits is possible if an abundance of food is avail- 

 able — such a supply, for example, as would accumulate if the downward 

 movement of sap were inhibited. Ewert assumes that fruit formation 

 on a tree occurs under competition for organic food. Such food, he thinks, 

 has a greater tendency to flow to those fruits that contain seeds, which 

 in turn are the result of cross-pollination. Consequently, seedless fruits 

 developing on the same tree with fruits containing seeds are handicapped, 

 and if the food supply proves inadequate such fruits will eventually 

 fall off. 



Inclosing the flower spurs in sacks is said by Ewert to bring about 

 unfavorable conditions for nutrition. Fruits developed on such inclosed 

 spurs, which must be self-polHnated if pollinated at all and which conse- 

 quently produce very poor seeds, are therefore handicapped in their 

 development. If the ability of a tree to set fruit without pollination 

 is to be determined, it therefore becomes necessary to prevent pollination 

 on all flowers and not merely on a few. When this precaution was 

 observed Ewert obtained seedless fruits which were as large as normal 

 specimens. He found, however, that the same variety was less likely 

 to set parthenocarpically when some of the flowers on the tree were exposed 

 to cross-pollination. 



Ewert found also that the dicogamy of the flowers is not always asso- 

 ciated with self -sterility, nor is the absence of this condition, which would 

 favor self-pollination, strictly associated with self-fertility. He believes 

 that the question of the need for cross-pollination in fruit setting has been 

 overemphasized. He is of the opinion that cold, rainy weather at bloom- 

 ing time is unfavorable to the setting of fruit, not so much because it 

 hinders fertilization as because such conditions are generally harmful to 

 the development of the young fruit. 



Osterwalder (1907 a, 1909) has also given the question of ])remature 

 drop considerable attention. His studies of the seeds of fruits that remain 



163 



