PROTOBASIDIOMYCETES 395 



however, effected by a dissolution of the upper portion of the cell 

 walls in contact, thus securing a union of two cells. From these 

 united cells, with two nuclei, as a basal structure arise the chain of 

 spores as before. The evidence offered seems to thoroughly explain 

 the origin of the binucleate condition. While there are many 

 exceptions which might be noted, there is in general, in the case 

 of a species showing all spore types, the following nuclear life 

 history. The mycelium which produces the spermogonia and the 

 aecidium is uninucleate. There is a fusion of cells in the aecidium 

 (where such organ is present) and the aecidiospores are binucleate. 

 The mycelium which produces the uredospores and the teleuto- 

 spores is. binucleate, and these spores are themselves binucleate 

 (in this type). Fusion of the nuclei results at about the time of ger- 

 mination of the teleutospore, so that the sporidia are uninucleate. 

 It is, however, unnecessary here to enter into a more detailed dis- 

 cussion of these phenomena. 



IV. CLOVER RUST 

 Uromyces Trifolii (Hedw.) Lev. 



HOWELL, J. K. The Clover Rust. Cornell Agl. Exp. Sta. Built. 24: 129- 



139. 1890. 

 PAMMEL, L. H. Clover Rust Iowa Agl. Exp. Sta. Built. 13: 51-55. 1891. 



Habitat relations. The clover rust is ordinarily a common 

 disease of various species of Trifolium. It causes a disease of the 

 clovers more serious in many instances than that produced by 

 Pseudopeziza, already mentioned. The Uromyces is cosmopolitan, 

 and the more susceptible hosts are important forage plants. Among 

 the clovers the following species are frequently infested : red clover 

 (Trifolium pratense), hybrid clover (Trifolium hybridum), white 

 clover (Trifolium repens), and crimson clover (Trifolium incar- 

 natum). The prevalence of the disease apparently varies greatly 

 with the season, and is to a considerable extent determined by the 

 spring conditions. We have, however, no very accurate knowledge 

 of the climatic relations of this fungus. 



This fungus is taken as a type of an autoecious member of the 

 genus, as it may have all stages on the same host plant. The 

 various stages commonly occur upon Trifolium repens and also 



