1913] MARTIN—POLLEN OF TRIFOLIUM PRATENSE 123 
tables show that for these temperatures germination takes place 
only when the percentage of moisture is close to saturation. 
The influence of the stigma upon the germination of the pollen 
and upon the direction of the pollen tubes 
The stigma presents a very uneven surface due to the projec- 
tion of the papillae. The exposed portion of the papillae has a 
rather heavy cutinized wall. Microchemical tests showed no 
sugar or starches present in the papillae, but an oily emulsion such 
as was found in the pollen. 
Although decoctions of the stigmas had been tried without any 
positive results, it was thought worth while to try them in connec- 
tion with the bladder. After the pollen had been spread on the 
prepared sections of bladder, stigmas from other plants were pressed 
down on these membranes with a scalpel, and then the sets were 
run under the bell jar on the laboratory table. These stigmas 
apparently exerted no influence on germination or on the direction 
of the pollen tubes. Often there was no germination around the 
stigma when there was good germination in other regions; and 
when there was germination around the stigma, germination just 
as good could be found in other places. The pollen tubes around 
the stigmas were grown in all directions, and pollen grains in con- 
tact with the stigma were found growing tubes at right angles to, 
and away from, the stigma. From these observations it appears 
that the stigma secretes nothing that has any effect on germination 
or the direction of the pollen tube. The behavior of the stigma 
in the experiments at least indicates that its function in the germi- 
nation of the pollen is to regulate the water supply; and the nature 
of the pollen necessitates no other function. If this is the function 
of the stigma, and the water supply must be as delicately adjusted 
on the stigma as on the membrane to secure germination, then 
conditions which will modify the amount of water delivered by the 
stigma will have an effect on fertilization and hence on seed pro- 
duction. This may account for the usually poor seed production 
in the early part of the season, since there is usually more moisture 
in the ground at this time and more rain during the flowering 
period than occurs during the second crop. If germination depends 
