784. H. E. KNnowutTon 
Resistance of pollen to extremes in temperature 
The results obtained by various workers show that pollen is very 
resistant to low temperatures. It is much less sensitive than the stigma. 
Goff (1901) found that plum and cherry pollen germinated after exposure 
to a temperature of —20° C.; raspberry pollen withstood a temperature of 
—23° C. Pollen of plum and cherry, confined for five days at a temper- 
ature of 20° C. in a saturated atmosphere, failed to germinate, while 
at 10° C. they germinated freely. Goff concluded from this that if the 
weather remained cool, a prolonged rainy spell would not be as injurious 
as at a higher temperature. 
Ewert (1911) subjected apricot and peach pollen to a temperature of 
from —8° to —15° C. for a period of from two to three hours. The results 
were not uniform, altho high resistance was shown. 
Sandsten (1910) found that freezing did not seriously injure apple, 
pear, and plum pollen, while less than 50 per cent each of the peach 
and apricot pollen’ were killed. A temperature of —1° C. caused perma- 
nent injury to the stigma of apple, pear, peach, plum, and cherry. 
Chandler (1913) determined that apple pollen, when dried, would 
withstand a temperature as low as from —8° to —13° C. for eighteen hours. 
At —4° C. apple and cherry stigmas were killed, and of the peach stig- 
mas, 43 per cent were killed at that temperature. 
The low water content of Antirrhinum pollen suggests that it possesses 
considerable resisting power to low temperatures. The success attending 
the storage at freezing temperature, and even at a temperature of —30° C., 
led the author to try lower temperatures. Pollen was placed in stoppered 
test tubes and frozen in liquid air, with the results shown in table 31: 
TABLE 31. Resistance or ANTIRRHINUM POLLEN TO TEMPERATURE OF Liqurp AIR 
15 
60 
IS 
60 
30 
60 
imeyins liquid’ ain i(mimiutes) rte asc eeeiseeiads 5 
Germination (percent) Meera eee a he see ce 
* After being in an ice-salt mixture for 30 minutes. 
The germination was equally vigorous in all treatments, and even 
longer germ tubes were produced by pollen which had been frozen. The 
rate of the fall in temperature had no effect. No pollinations were made, 
but since germination was so vigorous the pollen undoubtedly was able 
