FUNGI. 231 



fungus in addition ; so that it is not difficult to get 

 specinfiens. 



Sugar, as well as perfume, is occasionally secreted 

 with the spores. These, like the colour, are undoubtedly- 

 intended to attract insects. No less than i 3 5 species 

 of flies have been seen visiting one of the Euphorbia Rusts. 

 The spores have also been found in the footprints, left 

 by flies on window panes after they had visited the 

 fungus. The spores are also to be found in the air 

 and have been detected in dust samples taken from 

 greenhouse shutters. 



There are several interesting points connected with 

 the mode of life of these rusts of plants. The species 

 are very peculiar, considered as species. Forms which 

 appear absolutely identical are to be found living on 

 allied plants ; but the spores of the Rust {Puccinia 

 graininis), living on wheat will not infect barley or 

 couch grass, and those of the same fungus on barley 

 will not infect wheat. Even more remarkable is the 

 manner in which they migrate with the season. The 

 classical example, Puccinia graminis, lives on the corn 

 during summer and spreads from corn to corn by 

 orange spores. In autumn the fungus produces hard 

 black double spores which rest all winter on the ground. 

 As soon as the Barberry leaves are out, tiny wind- 

 blown spores are formed from these black spores which 

 are carried to, and infect the barberry leaves. They 

 produce very peculiar cup-like spots, orange-red in 

 colour, on the under surface of the leaf The Aecidio- 

 spores formed in these cups carry the disease from 

 Barberry to Barberry and then back to the corn. Their 

 life is thus like that of those hotel attendants, who migrate 

 from the Riviera to Switzerland, and so obtain support 

 from different sets of tourists. Coleosporium senecionis 



