204 THE STRAWBERRY IN NORTH AMERICA 



may be used. They should be tied closely at the bottom. 

 Pollen-carrying insects are not present in the greenhouse, 

 yet currents of air may distribute the pollen to some ex- 

 tent. If care is used in watering and ventilating, practi- 

 cal isolation is secured by separating the male and female 

 plants several feet. 



If only a few crosses are to be made, pollen may be 

 secured from the fully opened blossoms of the male 

 plant and transferred directly to the pistils, provided 

 both mature at the same time. When many crosses are 

 to be made, and the blossoms of the male parent mature 



FIG. 24. Anthers clipped off and exposed to the sun, to secure pollen. 



a few days earlier than those of the female, the pollen 

 should be secured beforehand. A large number of fully 

 developed anthers are clipped off closely and exposed 

 to the sun upon sheets of paper (Fig. 24). The anthers 

 soon burst; then most of them may be winnowed off, 

 leaving the dry pollen. This is preserved until needed 

 in small paper envelopes or vials ; if kept in bottles, these 

 should not be corked, as pollen ferments easily. C. S. 

 Crandall finds that the maximum period that strawberry 

 pollen will retain its viability is fifteen days. 1 



1 Proc. Soc. Hort. Sci., 9 (1912), pp. 121-30. 



