392 IOWA ACADEMY OF SCIENCE Vol. XXV, 1218 



time can be saved in experimental work involving artificial pol- 

 lination. Keeping- flowers enclosed in bags during pollinating' 

 experiments may have considerable effect upon the germination 

 of the pollen. The air enclosed in the bag becomes moist due to 

 the transpiration from the flowers and, if the germination of tlie 

 pollen is delicately adjusted to a certain amount of moisture, in- 

 creasing the atmospheric moisture about the stigma may have an 

 effect upon the germination of the pollen. 



The apples included in the investigation were Ben Davis, 

 Gano, Wealthy, Dutchess, and Jonathan. The Winesap was in- 

 cluded at first but it was found to have very little normal pollen 

 and was discarded. The investigations extended over three con- 

 secutive seasons which differed considerably in the character of 

 the weather as to rainfall and temperature during the blooming 

 period, but the requirements for the germination of the pollen 

 and the average percentages of germination obtained under the 

 same experimental conditions were practically uniform for the 

 three seasons. The flowers were collected from the same trees 

 each season and from one tree of each variety. It was not a part 

 of the investigation to determine whether or not different trees 

 of the same variety differ in respect to the germination of their 

 pollen. 



SIZE AND SHAPE OF POLLEN. 



Excepting the slight bulging of the germ pores, apple pollen 

 in the varieties studied is nearly globular when turgid, and. 

 when measured in a 5 per cent cane sugar solution, ranges in 

 diameter from 34-" tu 46m in Ben Davis, Wealthy, and Dutchess, 

 and 30i" to 38/^ in the Jonathan and Gano. 



Apple pollen loses water very rapidly when exposed to the air, 

 and in a few minutes the wall folds as a result of shrinking, as 

 showai in figure 163. In this condition on? diameter is very 

 much shortened and the other somewhat lengthened. Compara- 

 tive measurements of pollen in this condition are not reliable be- 

 cause the dimensions vary with the amount of shrinking of the 

 contents and the folding of the walls. Pollen shrinks so rapidly 

 that under ordinaiy pollinating conditions, it is shrunken when 

 it reaches the stigma. Examinations of pollinated stigmas 

 showed them covered with pollen in the shrunken condition. 

 CONTENT OF THE POLLEN. 



In the yomig bud, three or more days before the flowers 

 opened, the pollen grains contained much starch as shown in 



