512 FUNDAMENTALS OF FRUIT PRODUCTION 



other individual. The offspring of Brazihan plants became in England 

 in a single generation partially self fertile, and still more so in the second 

 generation. Conversely, the offspring of English plants, after growing 

 for two seasons in Brazil, became in the first generation quite self sterile." 



Season. — Just as it is almost impossible to separate the influence on 

 fruit setting of nutritive conditions within the plant from those of nutrient 

 supply without, so it is almost impossible to distinguish the influence of 

 locality from that of season. Seasonal variations at the same place may 

 give rise to practically the same changes in environment as are occasioned 

 by differences in localities during a single season. When this is true 

 approximately the same responses to the changed conditions would be 

 expected. Darwin^^ stated that Kolreuter had several plants of Verhas- 

 cum phoeniceum that for 2 years flowered freely and, though self sterile, 

 were interfertile with other plants, but that later "assumed a strangely 

 fluctuating condition, being temporarily sterile on the male or female 

 side, or on both sides, and sometimes fertile on both sides; but two of the 

 plants were perfectly fertile throughout the summer." Trees of the 

 native plum varieties have been found to vary greatly in fertility from 

 season to season^^ and a plum variety that is protandrous one season 

 may be protogynous the next."* 



An interesting case of a return of the potato to the fertile condition 

 through seasonal influences has been observed in the Greeley district of 

 Colorado.*^ The Pearl variety as grown in that section usually pro- 

 duces no flowers. During seasons that are unfavorable for the normal 

 development of the plant and its tubers, however, flowers are formed on 

 the late branches. Though ordinarily the blossom buds of the potato 

 fall off, in this case they opened but no pollen was produced. Thus the 

 degeneracy from the standpoint of the potato grower is accompanied by 

 some added development in the direction of fruitfulness. A ''bastard" 

 type is described as occurring sometimes in the Greeley fields of this 

 variety; in this there is still further degeneration of the tuber-bearing 

 habit, but an abundance of potent pollen is produced. 



End-season Fertility. — End-season fertility of normally self sterile 

 plants is rather common. Whitten^^^ reports that, "during 1897, Ideal, 

 a hybrid (grape) variety, proved to be self impotent early in the season 

 but self potent later on, the season being favorable to a succession of 

 bloom throughout the summer." He states that since the vine had 

 little fruit to carry, it made a vigorous growth and bore a succession of 

 flowers. The appearance of the self fertile condition late in the season 

 was accompanied by an increasing uprightness of the stamens and pre- 

 sumably with the formation of good instead of sterile pollen. A gradual 

 decrease in the percentage of defective mango pollen has been noted as 

 the season advanced. ^''^ East and Park^^ found end-season fertility 

 developing in their self sterile Nicotiana plants. In this case the imme- 



