METHODS 195 



dung-agar. Before the spores were sown, the places where they 

 were to be deposited were marked by means of small circles made 

 with a blue wax pencil on the glass surface of the bottom of the 

 plate. About 90 per cent, of the spores germinated. 



When the spores had been in the dung-agar about 24 hours or 

 longer and had produced germ-tubes or young myceUa, they were 



Fig. 111. — Coprinus lagopus, a heterothallic Hymenomycete. Two haploid mycelia, 

 each derived from a single basidiospore and growing on cleared diing-agar in 

 the middle of a large Petri dish ; photographed against a black backgroimd. 

 The one on the left was No. 1 of Table I and had the sexual constitution {Ab), 

 and the one on the right was No. 9 of Table I and had the sexual constitution 

 {aB). The darkness of the central part of each myceliimi is due to the surface 

 liyphae there having become largely or wholly immersed in water excreted by 

 the very mmierous oidiophores (cf. Fig. 116). More water has been excreted, 

 and probably more oidia have been produced, in the left mycelium than in the 

 right. Photograph taken seven days and seven hours after the inoculation of 

 each of the plates with a tiny mass of aerial hyphae taken from mycelia growing 

 on other plates. The radial rate of growth of the left mycelium (.46) was 

 0-14 mm. per hour, and that of the right mycelium {aB) was 0-13 mm. per 

 hour. Natural size. 



transferred with a piece of the dung-agar in which they were situated 

 by means of a flattened nicrome wire loop one by one to separate 

 Petri dishes containing dung-agar. There these monosporous 

 mycelia grew well ; and, after an interval of about four days, they 

 were ready for use in mating experiments (c/. Fig. 111). When 

 growing, they were kept at room temperature in the light in stacks 

 under a bell- jar. 



The dung-agar used as a culture medium was prepared as follows : 

 About 200 grams of fresh horse dung were stirred up in a granite 



