552 
Journal of Agricultural Research 
Vol. XXIV, No. 7 
Tabi,^ VII .—Summary of differences in the means of urediniospores 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 tritici and P. graminis secalis . 
5. 26±0. 24 
2. 6odbo. 08 
21.92 
32-50 
P. graminis tritici and P, graminis avenae . 
P. graminis tritici and P. graminis phlei- 
3. 90± . 24 
• iS± -09 
16. 25 
1.67 
pratensis . 
8. 45 ± .22 
2. 9I± .08 
38.38 
36. 38 
P. graminis tritici and P. graminis agrostis . 
10. 03 ± .22 
4. 11 ± .08 
46. 82 
51. 38 
P. graminis secalis and P. graminis avenae . 
P. graminis secalis and P. graminis phlei- 
I. 36± . 21 
2. 75± .09 
6.48 
30 . 56 
pratensis . 
3. i9± . 18 
.3idb .08 
17. 72 
3.88 
P. graminis secalis and P. graminis agrostis 
P. graminis avenae and P. graminis phlei- 
4- 77± • 18 
I. 5i± . 08 
26. 50 
18. 88 
pratensis ..... 
4 - 5 S± • 19 
3. o6± .09 
23. 93 
34.00 
P. graminis avenue and P. graminis agrostis 
P. graminis phleipratensis and P. graminis 
6. i3± . 19 
4. 26dz . 09 
32.25 
47 - 34 
agrostis . 
I, s8zb . 17 
I. 2o± . 08 
9 - 39 
15. 00 
Fig. s. —Differences in lengths of teliospores of biologic fomB of Puccinia 
graminis grown on congenial host plants and under uniform cultmal 
conditions. 
TEWOSPORieS 
Published data on teliospore dimensions can be found concerning only 
one biologic form of stem rust and that is timothy rust. The evident rea¬ 
son is because this form had been considered a distinct species. The other 
data available refer to the species P. graminis as a unit. The various 
authors consulted agree on the range in the size of teliospores of timothy 
rust. This is given as 38-52 X 14-16/4. Most authors, however, disagree 
on the size limits of the teliospores of P. graminis^ perhaps on account of a 
difference in the biologic forms which had been studied. The curves 
plotted in figures 5 and 6 point to the existence of a difference in size of 
the teliospores of the various biologic forms. In general there seems to be 
a fairly distinct parallellism in the size of the teliospores of the various 
