﻿BOTANICAL GAZETTE 



At 20° C. the average rate of growth of the pollen tube of apple 

 was 280 n for the first hour and 420 fx for the second hour. These 

 rates of growth were much more rapid than any observed by me, 

 but the optimum temperature agrees with my results, although 

 23 0 C. was the highest that I experimented with. Sandsten 

 found that after exposure to a temperature of — 1?5 C. for 6 hours 

 there was only a slight falling off in the germination of apple, pear, 

 and plum pollen, while in cherry and peach the falling off in the 

 germination was much more marked. 



Chandler (6) exposed the pollen of Jonathan apple to a tem- 

 perature of — 3 0 C. for 18 hours and found that in a 10 per cent 

 solution of sugar it gave a germination of 33 per cent. After 

 exposure of dried pollen of the same variety to a temperature of 

 — 13 0 C. for 18 hours it gave a germination of 20 per cent. Sand- 

 sten found that exposure of the stigmas of the five species men- 

 tioned above to a temperature of — 1?5 C. for 6 hours caused the 

 death of almost all of them. 



Finally, as regards the length of time during which pollen 

 grains can retain their vitality, Sandsten states that a small per- 

 centage of apple pollen retained its vitality for 6 months, while 

 but few pollen grains of plum retained their germinating powers 

 for this length of time. Both were kept dry at a temperature 

 ranging between 7 and 26 0 C. In my experiments a few pollen 

 grains of apple germinated after nearly 3 months, and of pear after 

 2 months, but no tests were made after longer intervals than these. 

 It is very probable that Sandsten's definition of what constitutes 

 germination was different from mine. Crandall (4), taking 

 fruit setting as the basis for determining the vitality of pollen, 

 found that the maximum age at which pollen was successfully used 

 was 11 days for apple and about 16 days for strawberry. 



Summary 



1. The following species were used for experiment: apple, pear, 

 strawberry, loganberry, raspberry, black currant. 



2. The culture medium was cane sugar and the strengths that 

 gave the best germination were as follows: apple 2.5-10 per cent, 

 pear 4-8 per cent, strawberry 8 per cent, loganberry 4 per cent, 

 raspberry 16 per cent, black currant 16 per cent. 



