British Fiuioi, 



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these sclerotia are met witli iu many different families, 

 and vary ia size from a mere point to that of a 

 cricket ball, and in some instances are very much 

 larger. In a species of Boletus found in West 

 Australia the underground mycelium forms a hard 

 sclerotioid mass, of a bright yellow colour^ extending 

 continuously for many squrre yards, and causes great 

 inconvenience, having to be broken up with a pick- 

 axe. Sclerotia may be looked upon as concentrations 

 of reserve material manufactured by the mycelium, 

 and often possesses the power of remaining dormant 

 for a long period, eventually under favourable con- 

 ditions producing spore-bearing structures, which not 

 unfrequently differ very considerably in appearance 

 and structure from those previously produced by the 

 myceliam forming the sclerotium. When dry, sclerotia 

 become hard and woody in texture, and on examin- 

 ing a tkin section under the microscope are found to 

 be composed of cells of various forms closely compacted 

 together ; but it is not difficult in general to trace 

 distinct hypha3 here and there, and the apparent 

 normal cellular-tissue appearance is in most cases due to 

 the fact that the component hyphge are so inextricably 

 interwoven to form the solid mass, that in a section, 

 taken in whatever direction, most of the hyphge are 

 cut in a direction more or less at right angles to the 

 axes of growth, which results in a section made up of 

 irregularly circular or elliptical cells. Nevertheless, 

 in some instances a sclerotium is built up after the 

 manner of true cellular tissue, and not from Ions', 

 interwoven hyph^, A minute black mould called 

 Ileterospormm aspratum, common on the leaves of 



