66 J. W. REED ON UROMYCES PISI. 



and shortening and thickening of the leaves are the usual result 

 of an attack by a Uredine. The mischief wrought in the host- 

 plant is consummated by the resultant abortion of the floral 

 organs, and their consequent sterility. 



I have also counted the ^cidia on my infected plants, and find 

 they average roughly about fifty to each leaf. They are about 

 one-third of a millimetre in diameter. A former President of 

 this Society, Dr. M. C. Cooke, once computed the number on a 

 leaf of the Yellow Goat's-beard {Tragapogon jyratensis) as 3,000 ; 

 even allowing for the great difference in the size of the leaf, the 

 u-^cidia on my specimens are not so numerous as this. Dr. 

 Cooke estimated that the individual u:Ecidium contained 250,000 

 spores, each of which, given suitable conditions, would be 

 sufficient to inoculate a healthy plant, and form a new centre 

 of disease. 



I am sorry that the sections I am exhibiting in connection with 

 this subject are not more successful ; I ought to have put the 

 fresh material into some preservative fluid there and then, and 

 not trusted to Herbarium material. This I found too dry, 

 crushed, and distorted, and, in cutting, it constantly tended to 

 crumble up. 



Uromyces pisi — as its specific name indicates, a pest to the pea- 

 grower — belongs to the Uredineaa, a large group of parasitic fungi 

 of which 400 or 500 species have been determined. The more 

 extreme abnormal growths brought about by the ^cidia of the 

 TJredineae on the host-plants are well illustrated by the bushy 

 excrescences popularly known as " Witches' Brooms " ; often seen 

 on the Silver Fir (Abies pecti7uitd), and other trees. Ustilago 

 esculenta, one of the Ustilaginese, causes considerable swelling 

 of the base of the stem of a species of grass, which, in this 

 abnormally succulent condition, is sold as a vegetable in the 

 Japanese markets. 



Less than a hundred years ago, had any one ventui^ed a state- 

 ment that certain fungi passed a part of their lives on one plant 

 and part on another not even remotely related botanically, it 

 would probably have been received with almost contemptuous 

 incredulity. Even up to a comparatively recent date the ^cidia, 

 or so-called " Cluster Cups," which, either seen in section or by 

 reflected light as opaque objects under the microscope, are so 

 beautiful and interesting, were regarded as a separate genus of 



