May 19,1923 
Statistical Study of Biologic Forms 
549 
to consider the differences between the agrostis and secalis forms as 
truly significant, although they might be considered as indicative. A 
greater number of measurements might possibly throw more light on 
this question. 
The following table gives the differences in the means of the aeciospores 
of the four biologic forms discussed in the preceding paragraphs, as well 
as the ratios between these differences and their probable errors. 
Af/0/^0/V^5' 
rio. 3.—Differences in lengths of nrediniospores of biologic forms of Puccinia 
graminis grown on congenial host plants and imder uniform cultural con¬ 
ditions. 
Table V .—Summary of differences in the means of aeciospores of biologic forms of P. 
graminis 
Biologic forms. 
Difference in means (in 
microns). 
Difference in 
means divided 
by probable error 
of the difference. 
Length. 
Width. 
Length. 
Width. 
P. graminis iritici and P. graminis secalis . 
P. graminis tritici and P. graminis avenae. 
P. graminis tritici and P, graminis agrostis. 
P. graminis secalis and P. graminis avenae. 
P. graminis secalis and P. graminis agrostis 
P. graminis avenae and P. graminis agrostis 
2. 62 io. 27 
I. lOzb . 22 
3. 26± . 26 
1. 52± . 22 
. 64± . 26 
2. i6± . 21 
2. 20±0. 15 
.96± . 14 
2. 68db . 13 
I. 24ih . 15 
. 48db .14 
I. 72± . 13 
9.71 
5.00 
12. 53 
6. 91 
2. 46 
10. 28 
14. 66 
6. 86 
20. 61 
8. 27 
3- 43 
13- 23 
UREDINIOSPORKS 
There is considerably more information found in literature on the rela¬ 
tive size of nrediniospores of biologic forms of P. graminis than on either 
aeciospore or teliospore dimensions. An interesting phenomenon of spore 
size relationship becomes apparent when the curves plotted in figures 
3 and 4 and-the data compiled from previous investigations are examined. 
