48 Journal of Agricultural Research voi. xvi.no.s 



MORPHOLOGY OF BIOLOGIC FORMS STUDIED 



The following biologic forms were investigated: Puccinia graminis 

 tritici Erikss. and Henn., P. graminis tritici-compacti Stak. and Piem,, 

 P. graminis secalis Erikss. and Henn., P. graminis avenae Erikss. and 

 Henn., P. graminis pMeipratensis (Erikss. and Henn.) Stak. and Piem. 

 and P. graminis agrostis Erikss. 



It has been stated by Stakman and Piemeisel {14, p. 484) that — 



In general, the size and shape of urediniospores of different biologic forms of Puccinia 

 graminis are similar. If, however, large numbers of spores are measured and the 

 arithmetical mean or biometrical mode is determined, it becomes quite apparent that 

 there are appreciable and fairly constant differences, provided the spores measured be 

 taken from congenial hosts. 



This was substantiated by the writers by many thousands of spore 

 measurements and careful computations. It is necessary, however, to 

 maintain uniform cultural conditions, since the range of variability in 

 size of urediniospores under different conditions is sufficiently great to 

 cause overlapping in some cases. A summary of the outstanding 

 morphological features of the urediniospores of the biologic forms studied 

 is given below. 



P. graminis tritici. — ^The urediniospores are quite constant in size, 

 shape, and color. They are the longest of all the biologic forms of 

 P. graminis, but in width they exceed only slightly those of P. graminis 

 avenae. Their shape is elliptic to ovoid, color light cadmium-yellow. 



P. graminis tritici-compacti. — The urediniospores are very similar to 

 those of P. graminis tritici, but are slightly shorter, and consequently 

 are inclined to be ellipsoid and oval. In color they are somewhat duller. 



P. graminis secalis. — The spores are uniform in size, color, and shape. 

 The color is dull, ashy yellowish to grayish; in length they are somewhat 

 shorter than those of P. graminis on oats, width approaching that of 

 spores of P. graminis phleipratensis; in shape cylindric-elliptic. 



P. graminis avenae. — ^The size and shape of the urediniospores are very 

 variable. The shape ranges from ellipsoid to ovoid to pyrifonn to sub- 

 plobose, even when grown on its type host, Avena sativa. Their color is 

 similar to that of spores of P. graminis tritici. 



P. graminis phleipratensis. — The spore shape is predominantly pyrif orm ; 

 they are very short and fairly uniform; their color is even duller and 

 more grayish than that of spores of P. graminis secalis. 



P. graminis agrostis. — ^The spores are remarkably constant in size, but 

 are smaller than those of any other form. In color and shape they 

 resemble spores of P. graminis phleipratensis, but possibly are not quite 

 so pyriform. 



The spore dimensions for the above biologic forms are given in Table 

 III, in order to faciUtate ready comparison. The "size limits" in this 

 table show the extreme variations of all of the urediniospore dimensions 



