May 19,1923 
Statistical Study of Biologic Forms 
559 
The aeciospores of the agrostis form on B, vulgaris possessed the 
following means: 16.46±0.18X 12.98±0.09 jit, while the means of these 
aeciospores on B. brevipaniculata were 13.72io.12X ii.86±o.07 /i. The 
difference between the two conditions, as shown in Table XI, is 12.45 times 
greater than the probable error for length and 10.18 times greater than 
that for width, which without any doubt is a very significant difference. 
Bromus tectorum L. produced a similar effect on the urediniospores of 
P. graminis avenae. The means of this biologic form on Avena sativa 
Fig. 8.-^Unifonmty in widths of aeciospores and urediniospores of biologic 
forms of Puccinia ffrantinis grown on different but equally susceptible 
host plants. 
were 28.50i0.15X i9-94io-07 while onB , tectorum they were 23.73 i 
0.16X 18.92 i 0.07 jLt. The difference in the means of the urediniospores 
in the two cases was 21.67 times its probable error for length and 10.20 
times for width; both are differences as significant as can be desired. 
The teliospores on the common wheat were over 5 fx longer than those 
on emmer, but practically the same in width. The means for the for¬ 
mer were 51.80i0.49X 16.67io.12 /z, while for the latter they were 
46.15io.32X 16.57io.12 fx. The difference in the means of the length 
only was significant. 
