PLATE 51 

 Cronartium ribicola: 



A. — A median section through a young uredinium forming in the space beneath a 

 stoma, a, Peridial cells; b, young urediniospores. The photomicrograph illustrates 

 a stage in the development of the uredinium midway between the stages shown in 

 Plate 51, B, and 55, B. X 650. 



B. — A section through the same uredinium as that shown in Plate 55, C, taken to 

 one side of the break in the peridium, toward the edge of the sorus. a, Peridial 

 cells; b, a yoimg urediniospore ; c, A stalk cell. X 525. 



C. — An internal tu-edinium from the cortex of Ribes hirtellum. X 315. 



