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its host. Under microscopic examination the infected cells show 

 no abnormal effects other than lack of chlorophyll. The Hous- 

 tonia rust shifts to another meadow plant. Blue-eyed grass, a 

 neighbor in the fields, is the teleutosporic host. (53) A summer 

 resident should certainly find it in Norton. 



Rust of carnations, although of greenhouse cultivation, 

 stands in our list since we find it frequently in nearby green- 

 houses. This cosmopolitan rust, a pest to carnation growers, 

 came from Europe and seems to have left behind its aecidial 

 host. (37) Indeed its claim to heteroecism (14) rests merely upon 

 the reports of a few cross inoculations from Euphorbia geradiana 

 to the carnation. (12) Both in Europe and America the rust 

 continues upon the carnation by means of its repeating spores, 

 the uredospores. For a fungus which can pass the winter under 

 glass no other spore form, and no alternate host is necessary. 



There are several single-host rusts at Wheaton. Hollyhock 

 rust which we met at the start is one, and asparagus rust. 

 Potentilla rust is another. As the March sun strikes along the 

 foundations of our brick buildings flecks of orange appear on 

 the green rosettes of the "five-finger" Potentilla. By April the 

 uredospores are so abundant that patches of Potentilla in the 

 turf near the rock garden seem touched with orange paint. 

 Uredospores of this rust act like aecidiospores in that a cell 

 fusion which precedes their formation gives them double 

 nuclei. (17) Here is introduced the fascinating, unsettled 

 question of sexual reproduction in the rusts. Structures which 

 produce egg cells have not been found in rust fungi. When in 

 certain rusts a fusion between cells (17) or in others a migration 

 of a nucleus into a cell at the base of an aecidium was discovered 

 (15), rusts were treated as examples of plants where a substitute 

 fusion had taken the place of fusion between sexual cells 

 developed on sexual structures. When Craige took his cue from 

 the chance fly in the planthouse and mixed the drops of sper- 

 mogonial fluid upon a rust-infected barberry leaf he discovered 

 that spermatia function in producing aecidiospores. (19) This 

 discovery that the spermatia, long considered functionless 

 spores, have a part to play in reproduction has renewed the 

 interest of botanists in bean rust (5, 6), in wheat rust on the 

 barberry (1, 2), in corn rust on Oxalis (50), in all spermogonial- 

 aecidial rust stages . . . but a discussion of this problem would 



