544 FUNDAMENTALS OF FRUIT PRODUCTION 



those that are self unfruitful are: Salem, Barry, Brighton and the follow- 

 ing are among those often at least partly self fruitful : Lindley, Vergennes, 

 Wyoming.^ 



Practically all the varieties of the Muscadine group bear pseudo- 

 hermaphroditic flowers and should have staminate vines interplanted 

 with them. 



The immediate factor responsible for self barrenness in the grape is the 

 production of impotent or sterile pollen which is incapable of fertilizing 

 the ovules of the same or of any other variety.^' ^^ Consequently self 

 barren varieties are interbarren and partly self barren sorts are partly 

 interbarren. Self fertile varieties should be interplanted with the self 

 barren or partly self barren kinds. The production of impotent or 

 sterile pollen is associated almost invariably with curved or reflexed 

 stamens; good pollen is produced in erect stamens. This flower character 

 therefore affords an accurate index to the degree of self fruitfulness that 

 may be anticipated, except in the comparatively few parthenocarpic 

 varieties. 



Many grape varieties occasionally produce a few seedless berries 

 when not polhnated or when pollinated with impotent pollen. This 

 characteristic apparently is aided by certain practices such as ringing or 

 girdhng. In a few varieties, such as Thompson's Seedless, this occurs 

 regularly .^^ According to Stout, ^^^ seedless American grape varieties 

 generally produce good pollen, but since their "femaleness" is not 

 strongly developed they are not able to mature good seeds. 



Strawberry. — Strawberry varieties are generally classed as pistillate 

 flowering and perfect flowering. Apparently all the perfect flowering 

 sorts produce good pollen and all are self fruitful and apparently any 

 perfect flowering variety may be planted with any pistillate flowering 

 sort for purposes of cross pollination. Since, however, some of the per- 

 fect flowering varieties produce only small amounts of pollen, they are 

 not ideal pollenizers for pistillate sorts. In general the later maturing 

 flowers of the inflorescence, particularly in the perfect flowering varieties, 

 are less fertile than earlier flowers of the same cluster and this pistil 

 sterility is "expressed in the production of irregularly shaped berries or 

 entirely sterile flowers." ^^^ 



Currant and Gooseberry. — Few exact data are available on the polli- 

 nation requirements of the currant and the gooseberry. However, field 

 observation indicates clearly that the varieties commonly grown in this 

 country are self fruitful and hence no provision need be made for cross 

 poflination. Hooper^^ has reported all the varieties of the English goose- 

 berry which he tested to be self fertile. 



The Brambles. — Until comparatively recent date the bramble fruits 

 have generally been considered self fruitful. Hooper,''^ working with a 

 number of varieties of the raspberry and with the loganberry in England, 



