236 Massee : Polymorphism in Fungi. 



In many instances these different stages all grow on the 

 same substance and at the same spot, following each other in 

 the proper sequence. In numerous other instances, as in the 

 rusts and mildews of cereals and other plants, different stages 

 of the fungi grow on totally different kinds of plants, the spores 

 or reproductive bodies of one stage being usually conveyed by 

 wind from one host-plant to another. In other instances, 

 insects are the agents that convey the spores produced by one 

 stage to the place where infection is necessary to produce the 

 following stage. This occurs, for example, in a fungus called 

 Sclerotinia heteroica, one stage of which grows on the young 

 leaves of V accinium iiliginosum. The spores produced by this 

 form of the fungus are unconsciously conveyed by insects, and 

 deposited on the stigmas of Ledum palustre. It may be necessary 

 to explain this transportation of spores on the part of insects, 

 which is entirely due to the fact that insects, in common with 

 other living organisms, must eat to live. The form of the fungus 

 growing on Vaccinium leaves, which resembles a minute white 

 mould, secretes a sweet, scented substance, approved of by 

 certain small insects as food. While partaking of this food, the 

 proboscis of the insect becomes dusted with the spores of 

 the fungus. The flowers of Ledum palustre also contain some- 

 thing that can be utilised by the same insect, and is accordingly 

 visited in turn. In the act of obtaining the nectar, the spores 

 adhering to the proboscis of the insect are deposited on the 

 stigma of the Ledum flower. This appears to be entirely a 

 matter of chance, but the chance obviously happens sufficiently 

 often to secure the continuance in fair abundance of the fungus 

 under consideration. The spores deposited on the stigma of 

 Ledum germinate quickly, grow down the style, and enter the 

 ovary, where a dense mass of mycelium or spawn is formed. 

 This spawn remains in a resting condition until the following 

 spring, when it gives origin to spore-bearing bodies resembling 

 miniature champagne glasses, supported on long stalks. The 

 spores from these structures are dispersed by wind, and those 

 that happen to alight on the young leaves of Vaccinium set up 

 infection, which results in the production of the first mould- 

 like condition of the fungus. What at first sight might be 

 considered as a series of coincidences connected with the life- 

 history of the fungus briefly detailed above, must be considered 

 as part of the scheme of evolution and struggle for existence 

 on the part of the fungus. Both its host-plants sufter from 



_^ Naturalist, 



