286 



POMOLOGY 



the germination of apple and plum pollen, or on the rate of 

 growth of the pollen-tube. These tests refer to the artifi- 

 ficial germination of pollen-grains in various media. It is well 

 known that blossoms will be fertilized and the petals fall 

 much more quickly in bright than in cloudy weather. The 

 following data support the above conclusions in regard to 

 germination : 



Table LXXXIV 

 percentage of germination and rate of growth of pollen in 



SUNSHINE AND CLOUDINESS (aFTER SANDSTEN) 



The rate of growth of the pollen-tube appears to be read- 

 ily affected by low temperature and, therefore, actual fer- 

 tilization may be delayed some seasons more than others 

 by several days. Sandsten reported that "Under favorable 

 conditions it requires nine to thirty-two hours for the pollen 

 tube of apples, plums, and cherries to reach the ovary when 

 placed on the stigma or in the germinating medium. Cherry 

 pollen requires a little over 12 hours. Two or three bright 

 days at the time of full bloom is sufficient for the setting of 

 the fruit." Dorsey questions these observations in regard 

 to the plum and thinks the time would be greater, as much 

 as eight to ten days under some conditions. 



Goff has shown that "Plum pollen does not germinate 

 at temperatures below 40° F., and even at temperatures as 

 high as 51° F. that there is slow pollen tube growth." 

 ' Medium, a 3 per cent cane-sugar solution. 



