POLLINATION AND STERILITY 289 



peach and apricot pollen grains were killed by this tempera- 

 ture." The lack of cultivation and fertility in orchards 

 greatly injures the production and fertility of pollen. 



From these investigations it can be seen that the pollen 

 of the apple, plum, peach, and cheriy, (and it can be added 

 for other fruits as well) will remain viable throughout the 

 period of blooming and probal:)ly for a much longer time if 

 kept \mder ordinary conditions of temperature and humidity. 



257. Length of receptive condition of the stigma. — In 

 contrast to the surprisingly long time that pollen is viable 

 and capable of germination and to the untoward conditions 

 that it can withstand, the ]iistils are most delicate and of 

 short duration. They are readily susceptible to mechanical 

 injury as well as to damage from inclement weather. There 

 is some question as to whether a stigma has more than one 

 period of active secretion; in some cases there is only one, 

 while other observers have held that more than one occurs. 

 The pistils are sensitive to cold and are often injured when 

 other floral parts are unhurt. Frosts or drying winds may 

 cause a loss of the whole or a part of the fruit crop if they 

 occur when the blossoms are open. 



Waugh ^ found that the stigmas of plums are receptive 

 "From four to six days if pollen is withheld and conditions 

 are favorable. If pollen is abundant they are almost im- 

 mediately pollinated and cease to be receptive." Dorsey 

 found that "under normal conditions, the plum stigma re- 

 mains receptive for a maximum period of about one week, 

 but usually from four to six days." 



258. Fertilization. — The process of fertilization may be 

 briefly stated in this connection since the whole problem of 

 fertility and sterility of orchard fruits is intimately associa- 

 ted with it. When the pollen-grain or microspore is formed, 

 it possesses two nuclei, one known as the tube (vegetative) 



1 Vt. Agr. Exp. Sta. 11th Ann. Rept. 1897-1898. p. 258. 



