J. W. REED ON UROMYCES PISI. 69 



" The mycelium o£ the secidium or * cluster-cup ' stage of 

 Uromyces pisi (De Bary) is perennial in the tissues of the host ; 

 hence, when plants are once attacked they never recover, but 

 produce the fungus year by year. The secidiospores, produced in 

 the ' cluster-cups,' are dispersed by wind at maturity, and those 

 that happen to alight on a leaf of the common pea (Pisitm 

 sativum) germinate within a few hours if the surface of the leaf 

 is damp ; the germ-tube bores through the epidermis, enters the 

 tissues of the leaf and there forms a mycelium.* About fourteen 

 days after infection, the mycelium produces dense tufts of 

 uredospores, which burst through the epidermis at maturity, 

 and are distributed by wind and rain. Those uredospores that 

 alight on pea-leaves germinate quickly, enter the tissues of the 

 leaf, and, in turn, produce other clusters of uredospores. The 

 clusters of uredospores are pale brown. Uredospores are called 

 summer-spores, their function being to enable the fungus to 

 extend its area of distribution. Produced in enormous quan- 

 tities, and very rapidly throughout the summer, it is easy to 

 understand the swiftness with which the disease can, and does 

 spread; the only limit being lack of supply of pea-plants for 

 it to attack. 



" In the autumn, when the host-plant is waning, a second form 

 of spore is produced from the same mycelium that produced the 

 uredospores earlier in the season. This second form of spore is 

 known as a teleutospore, or winter spore, and differs from the 

 uredospore in requiring to remain in a latent condition before 

 it can germinate. The function of teleutospores is to tide the 

 fungus over that part of the season — its season of discontent — 

 when the host-plant is not present for it to prey upon. After 

 remaining in a resting-stage during the winter, the teleutospores 

 germinate in the spring, and give origin to still smaller spores 

 called sporidiola or secondary spores. These exceedingly minute 

 secondary spores are, as usual, dispersed by wind, and those that 



* This mycelium, or vegetative portion of the fungus, consists, as will be 

 well known to most of our members, of a network of anastomosing and 

 transparent tubes. These tubes, containing protoplasm, are divided b}^ 

 septa at rare intervals into elongated cells. The septa become more 

 frequent at the points where sori are formed, and, in Uromyces imi and 

 other species producing spores of that colour, orange granules appear in 

 the protoplasm. — J. W. E. 



