52 IOWA ACADEMY OF SCIENCE 



Magnitudes 9 cm., .91 cm., .92 cm., .93 cm., .94 cm., .95 cm. 



Frequencies 87, " 39, 49, 4, 17, 29, 



Magnitudes 96 cm., .97 cm., .98 cm., .99 cm., 1. cm. 



Frequencies 28 1, 7, 1, 5, 



Tlie length was found to vary from .6 cm. to 1. cm., with the mode at Class 

 10 (.88— .9). 



CONSTANTS. 



n=493 Number of flowers. 



A=.8918 Mean length. 



S=.1494 Index of variability. 



C=.16751 Coefficient of variability. 

 Ea=. 0045306 Probable error of mean. 



E5=2.9524 Probable error of index. 



Ec=. 041707 Probable error of coefficient. 



For use in plotting a curve the magnitudes were seriated into 14 

 classes, each class a group of three magnitudes, from .6 cm. to 1.02 

 cm., supplying ommissions with ciphers. The mode lies at class 10 

 (group .88-.9 cm.) it is quite regular and not wide, and is abrupt in 

 the direction of greater dimension. 



The magnitudes are seriated into classes as follows: 



Size of Pollen Grains of Red Clover. 



A study of pollen grains was made from red clover blossoms gath- 

 ered miscellaneously at Ames in October, 1910, to determine variations 

 in width and length of grains. Four to six counts were made from 

 each head. Measurements of 1,024 pollen grains were made, with the 

 micrometer scale, and curves constructed using units of this scale; 

 each unit represented 4:"^. 



