8 6 BASIDIOMYCE TES 



ply from the fact that the host plants affected happen to be of im- 

 portance themselves and the fungus in either stage detracts from 

 its free growth. The common wheat- rust commences its life his- 

 tory as a parasite on the barberry (Berberis); in May or June thick- 

 ened yellow spots appear on the leaves of the barberry and from 

 these a series of rounded yellowish bodies push their way through 

 the epidermis and open up as little cups or craters ; from their 

 habit of growth they have taken the name of cluster-cups. Be- 

 fore their true relations were known they were described as definite 

 fungus species under the name of Aecidhtm. The spores are 

 produced in chains, numbers of which are packed so closely 

 within the membranous pseudoperidium which covers them, as 

 to render them angular from pressure. These spores are one- 

 celled and thin-walled. They germinate in the presence of mois- 

 ture, but will come to naught unless they are carried by the wind 

 or otherwise to young plants of the wheat which they parasitize, 

 the mycelium from the germinating spore entering the host plant 

 through one of the stomata. Once inside, growth takes place and 

 in due time the mycelium accumulates under the epidermis and 

 there produces a mass of spores whose growth finally ruptures the 

 epidermis and appears as a sorus of one-celled, yellowish-brown 

 or rusty spores which have a deciduous stalk, and are made up of 

 a single cell. (PI. 6. f. j.) This stage is known as red rust by 

 the farmers and, like the cluster cup, was described, before its rela- 

 tions had been made out, as a member of a fungus genus, Uredo. 

 It is by means of these thin-celled summer spores that the wheat- 

 rust makes such havoc in a wheat field. The spores are loosened 

 from their stalks at maturity and are carried by the wind to other 

 wheat plants ; a few favorable sultry days will furnish the condi- 

 tions necessary for rapid germination and what was a single cen- 

 tre of infection has become a thousand, each rapidly producing 

 new crops of spores and continuing ever to widen the amount of 

 infection ; should this attack come at the time when the young 

 kernels of wheat were forming, the nutrition that would naturally 

 go to them would be absorbed by the mycelium of the fungus 

 and the kernels would become shriveled and worthless. A little 

 later either from the same sori in which the red rust spores were 

 produced or in others, black spores appear. These differ from 

 the preceding (i) In having a permanent stalk ; (2) In having 



