STUDIES IN POLLEN, WITH SPECIAL REFERENCE TO LONGEVITY 787 
The results from the storage experiments with pollen were exceedingly 
variable. Many factors that are difficult to control may influence the 
results. Pollen produced in different seasons and under diverse conditions 
is, in some way, physiologically different, as is shown by the differences 
in water content, the different optimum sugar concentrations required 
for germination, and the variations in the duration of life. Temperatures 
at pollination time, especially if unfavorable, may also influence results. 
It is an established horticultural fact that a larger “set” of fruit occurs 
on “‘ selfed ” varieties in seasons when the temperatures are most favorable 
for pollen tube growth. In the corn-storage experiments, where field 
experiments were made, it was, of course, impossible to control the 
temperature. In the Antirrhinum-pollen-storage experiments, all plants 
were grown in the greenhouse, so this factor was probably negligible. 
The difference in resistance of the two kinds of pollen to extremes of 
temperature was striking, altho it was about what one would expect. 
Corn pollen with a high water content and high respiratory activity was 
more susceptible to injury than was Antirrhinum pollen with its low water 
content and weak respiratory activity. If death is due to an irreversible 
change of the protoplasmic system, a protoplasm like that of Antirrhinum 
pollen would be more resistant because of its low water content and, 
consequently, more stable, gel-like emulsion. 
According to Harvey (1918), in addition to water content and meta- 
bolic activity, the basicity of the protoplasm also influences the resistance 
to low temperatures. In these studies, no hydrogen-ion determinations 
of pollen protoplasm were made. 
SUMMARY 
Pollen of snapdragon (Antirrhinum majus L.) germinates in any concen- 
tration of cane sugar up to 30 per cent. The most favorable concentration 
varies from 10 to 25 per cent, depending on the conditions under which 
the plant has been grown. 
The most favorable temperature for the germination of Antirrhinum 
pollen is about 25° C. 
The moisture content of Antirrhinum pollen varies from 10 to 20 per 
cent. ; 
Cane sugar is the chief reserve carbohydrate in Antirrhinum pollen, 
the amount ranging from 8 to 10 per cent of the fresh substance. 
