Corn Investigations 
47 
54, 56, and 58 hours after collecting the pollen, ten of the covered 
ears, having abundant silk development, were fertilized with 
this pollen. The relative viability of pollen at various ages is 
illustrated by the number of kernels fertilized on the ears shown 
in figure No. 11. Fertilization was very poor at the end of 51 
hours and failed after 58 hours. 
In 1920, fresh pollen was collected at 7 A. M. from 40 
tassels and was well mixed. This was immediately divided into 
10 paper bags which were tied to the tops of corn plants in the 
cornfield, where they remained until used. The temperature 
range was from 75° F. to 100° F. and the mean relative humid- 
ity ranged from 30 to 70 per cent. Ears pollinated with this 
pollen 10 and 15 hours after it was collected showed good fer- 
tilization; but the pollen had practically lost its viability at the 
end of 24 hours. Thus it may be inferred that pollen kept 
under such intermediate conditions will have lost its viability at 
the end of 20 to 60 hours after shedding. 
LIFE OF SILKS 
The life of the unfertilized silk is seldom a problem in ex- 
periments involving the artificial fertilization of corn. Control 
tests have indicated that silks are receptive to pollination before 
they have emerged from the husk, and for a period of two weeks 
thereafter. The earliest effective application of pollen in some 
instances necessitated opening the husks three or four inches to 
reach the silks. In other cases of delayed yet effective pollina- 
tion silks were exposed for a length of twelve inches. Silks 
continue to grow in length for some time if pollen is withheld. 
Such silks may be cut off to a short length and yet be success- 
fully pollinated. In controlled fertilization experiments which 
necessitate covering the young ears, it is important to keep 
them covered for some time after applying the pollen, in order 
to avoid the chance pollination of late receptive silks. 
Dr. E. C. Miller of the Kansas Agricultural Experiment 
Station has found by means of histological studies that fertili- 
zation of the kernel is effected within a period of about 24 hours 
after applying pollen to the silk. Thru similar studies, Dr. Paul 
Weatherwax of the University of Georgia estimates the lapse of 
time between pollination and fecundation at about twenty-five 
hours. Germination of the pollen on the silk is rather rapid. 
In our tests regarding this, the tip ends of the ear shoots were 
sterilized in alcohol six hours after pollination, and were cut off 
a short distance below the end of the husks in order to com- 
pletely remove the portion of the silks to which the pollen had 
been applied. The ears were kept covered to exclude further 
