May 19,1923 
Statistical Study of Biologic Forms 
547 
AECIOSPORES 
No previous record of aeciospore measurements of biologic forms of 
P. graminis could be found. The data available relate to the species as 
a whole, the assumption evidently having been that there was no differ¬ 
ence in the size of aeciospores of the various biologic forms. Figures i 
and 2, however, show at a glance the variation existing between different 
biologic forms at this juncture in their life cycle. The variation is greater 
in figure i, in which the curves for spore length are plotted. Here the 
class containing the greatest number of individuals in the P. graminis 
triad curve is greater by 4 ju than the identical class in the agrostis curve, 
greater by 3 ^ than that in the secalis curve, and greater by only i 
than the homologous class in the avenae curve. Figure 2 presents a 
somewhat different picture. In this graph which represents curves for 
spore width, the greatest difference between any two classes containing 
the largest number of individuals is 3 ju, viz, P. graminis tritici and P. 
graminis agfostis. In P. gfaminis secalis and P. graminis agrostis the 
modes fall at exactly the same point, i. e.,at 13 (i. An examination of 
the constants in the first section of Tables III and IV and of the differ¬ 
ences in the means as presented in Table V will reveal not only the exig¬ 
ence of a difference in the spore dimensions but in most cases also the 
distinct significance of such difference. 
