May 10, 1924 
Puccinia graminis in the United States 
545 
The mean length for teliospores of P. graminis poae is 3.40±0.74/x less than that 
for those of P. graminis agrostis , which formerly were considered the shortest of 
all. This difference is 4.59 times the probable error and therefore is significant 
statistically. According to the computations of Pearl and Miner ( 8 ), the odds 
against the occurrence of such a difference on account of random sampling are 
about 520 to 1. The mean length for aeciospores of P. graminis poae is only 
1.39 ± 0.20m less than that for those of the variety agrostis. But this difference is 
even more significant than the apparently greater difference between the means 
of the length of the teliospores of these varieties, because it is almost 7 times its 
probable error, and the odds against its chance occurrence are about 40,000 to 1. 
Of still greater significance is the difference between the means of the length of the 
urediniospores of these two varieties. It is more than 23 times its probable error, 
the actual difference being 3.73 ±0. 16m. 
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Fig. 2—Ratios of length to width of the various spores of Puccinia graminis poae arranged in classes 
The mean width of the teliospores of the poae variety is approximately the same 
as that of the varieties avenae and the phleipratensis , that of the aeciospores is 
similar to the mean width of the varieties secalis and agrostis , and that of the 
urediniospores is nearly the same as that of P. graminis agrostis. 
The variations in length and width of the various spores of Puccinia graminis 
poae are shown graphically in fig. 1. 
The ratio of length to width, as shown in fig. 2, was determined by the method 
suggested by Rosenbaum {10 , p. 250). The correlations of length and width 
of the three different kinds of spores are presented in Tables V, VI, and VII. 
The teliospores (PI. 1, B) of the variety poae appear to be extremely variable 
in shape. Some are very short and broad (27.14X20.01m) while others are 
greatly elongated and narrow (63.48X1 1.73m). The predominating ratio of 
length to width of the teliospores is about 2 to 1. There is a definite negative 
correlation (— .613±.0421) between the long and short diameters of these 
spores (Table V). 
