Srupies In POLLEN, WITH SPECIAL REFERENCE TO LONGEVITY 777 
In the experiments conducted in the summer of 1916, pollen was sub- 
jected to different moisture, as well as different temperature, conditions. 
The pollen was stored in bottles. The several percentages of moisture 
were obtained by drawing air thru different concentrations of sulfuric 
acid, according to the tables of Landolt-Bérnstein. Withdrawals and 
field pollinations were made as in the 1915 experiments. The percentage 
of fertilization was obtained by actually counting the fertilized and 
unfertilized ovules on each ear. 
TABLE 21. Corn Po.tuen Stored at 30° C. snp 20-30 Per Cent Humipiry. 1916 
Length of storage eae d Fertilization 
Hours Number Per cent 
Bo 6 0.66.00 OO USS AE ERIE CRS ES RE REEL AEM e te eACeaSrT pea es 1 
fl RRS ee acces ete he ler Sreisidte aidleva ie acach ited veeiey Dials 3 12 
Ph | 9.0:0'0.0.0.0 0 6.010 :0:08 LES CRORE CEDIA SHORE SII ee Sins Cre er 2 0 
5D) 5 o'0.6.0.6:0'6 0° OU ea Sree gt Retna Raita ine ons HI eal ee net ae 2 0 
Other storage experiments were made, but temperature conditions 
at pollination time were so unfavorable that the results were discarded. 
Under conditions of high humidity, moisture often collects on the 
pollen, causing the grains to swell and adhere to one another. On micro- 
Scopic examination, films of water are seen around the grains. This water 
does not come from the air, but is excreted by the pollen grains themselves. 
This is shown by the fact that this “‘ caked” pollen has not increased in 
weight. As individual pollen grains differ in the amount of colloids 
and in the concentration of osmotically active substances, it is possible 
that one grain extracts water from another. However, if this were true, 
one would expect some grains to be shrunken, which is not the case, so 
some other explanation must be found. Such changes as coagulation or 
precipitation of the proteins may take place within the protoplast, which 
would lessen its power to retain water. A secretion of water would then 
result. The caking of pollen impairs its viability and interferes with 
the mechanical operations of pollination. Caked pollen is also a favorable 
medium for the growth of molds and other fungi. 
