Aug. 27, 1917 Puccinia graminis 07i Cereals and Grasses 



485 



however, be done if the spores of the various biologic forms are devel- 

 oped on congenial hosts under similar conditions and if enough spores 

 are measured. The range of variability in size of urediniospores is suflfi- 

 c-iently great to cause overlapping in some cases unless conditions have 

 been uniform. A brief summary of the important characters of uredinio- 

 spores of the different biologic forms is given. The sizes are given in 

 Table XXXIV. 



P. graminis tritici. — The spores are quite constant in size, shape and 

 color. They are longer than those of any other forms, but in width they 

 are about the same as those of P. graminis avenae. Shape is elliptic to 

 ovate, color bright cadmium-yellow. 



P. graminis tritici compacti. — Quite similar to P, graminis tritici. 

 Color practically the same; spores slightly longer; shape, ovate to 

 ellipsoid. 



P. graminis secalis. — Uniform in size, shape and color. Shape elongate- 

 elliptic; in length somewhat shorter than urediniospores of P. graminis 

 avenae, in width approaching that of urediniospores of P. graminis phlei- 

 pratensis. Color dull yellow to grayish, similar to that of P. graminis 

 phleipratensis . 



P. graminis avenae. — Color bright cadmium-yellow; size and shape 

 very variable, shape ellipsoid, pyriform or globose. 



P. graminis phleipratensis. — Shape mostly pyriform; color dull yellow 

 to grayish ; size fairly uniform. 



P. graminis agrostis. — Spores very similar to those of P. graminis phlei- 

 pratensis, possibly not quite so dominantly pyriform and somewhat 

 smaller. 



In order to facilitate ready comparison the spore dimensioms are 

 grouped in Table XXXIV. 



Table XXXIV. — Coviparative sizes in microns of urediniospores of biologic forms of 



Puccinia graminis 



It will be readily seen from Table XXXIV that there is considerable 

 difference in the sizes of urediniospores of different biologic forms. Those 

 of P. graminis tritici are largest and those of P. graminis tritici compacti 

 differ only slightly. All the other forms are quite different, however, the 

 spores of both P. graminis avenae and P. graminis secalis being shorter. 



