298 POMOLOGY 



to fertilize one another, but are readily fertilized by the pol- 

 len of a still different variety. 



These various phenomena must not be confused with the 

 condition that exists in the case of imperfect flowers, such 

 as with some of the strawberries. Here there is an actual 

 lack of one of the essential organs (stamens). The term 

 morphological self-sterility may be applied to this case, which 

 is not infrequent with other fruits such as the grape and 

 mulberry. 



It has been shown that self-sterility is a heritable char- 

 acter but that it may be modified by changing the environ- 

 ment. Fvn-ther, a tobacco plant which is ordinarily self-sterile 

 may become partially fertile and produce a few seeds at the 

 end of a flowering period and under conditions adverse to 

 vegetative growth . ^ 



While not particularly related to the sterility problem, 

 the term parthenocarpy may here be defined. This indicates 

 fruits which develop wholly independently of any pollination 

 of the stigmas or fertilization of the ovules. The term refers 

 to the development of fruit structures other than the seeds. 

 This phenomenon is not uncommon with the apple and pear.- 



Another case of interest and quite unlike the above is 

 when the flesh of the fruit develops only if pollination of the 

 stigmas has taken place. Fertilization may or may not fol- 

 low pollination, but if so there is an abortion of the embiyos 

 at a more or less advanced stage and hence no viable seeds 

 develop. 



Thus, finally, all fruit-trees are classed as either barren or 

 fruitful, and if the former they are always sterile, whereas 



lEast, E. M., and J. B. Park. Studies on self -sterility. Genetics, 

 2:505-609. 1917. 



2 See Kraus, E. J., and H. R. Kraybill. Ore. Agr. Exp. Sta. Bull. 

 149. pp. 6-11. Also Sturtevant, E. Lewis. Seedless fruits. Mem. 

 Torrey Bot. Club, Vol. I, No. 4, 1890. 



