52 M. C. COOKE ON MICROSCOPIC MOULDS. 



a little common paste which has been exposed a few days, until the 

 surface has become covered with a ropy film. If we try to spread 

 a little of this paste upon paper we are soon convinced of its ropi- 

 ness, and the microscope reveals the cause. The surface of the 

 paste is covered with an interwoven layer of mycelium. It is 

 clearly the mycelium of a fungus, but whether it is a mould or 

 not, however much we may guess, nothing can be known. In the 

 course of two or three days discoloured patches — yellow, blue, or 

 green- — make their appearance. Tufts of woolly threads, some 

 barren, and like little tufts of cotton wool ; others of a denser 

 nature laden with minute spores. Everybody calls it " blue mould," 

 and there nearly everybody is content to leave it unmolested, so 

 far as any insight into its structure is concerned. 



Under a low power a tuft of this " blue mould " appears as a 

 forest of delicate white threads, with a brush-like tuft of spores at 

 their apices, and under a still higher power the white threads 

 are observed to be jointed or divided by transverse septa, and in 

 the extreme upper portion subdivided into a fascicle, or bunch of 

 short delicate branches, which tend upwards at an acute angle, and 

 are terminated by necklaces of spores, attached to each other like 

 beads, and thus forming a kind of inverted tassel of spores, con- 

 cealing the branches of the threads, so that nothing is seen but the 

 simple stem and its tassel. When the spores fall away the branches 

 are distinctly visible. This is one of the fungi to which the name 

 of " blue mould" is given, but as that name is also applied to other 

 moulds, we must perforce employ for the future a less ambiguous 

 term. There is a Latin word which" represents very well the ap- 

 pearance this little mould possesses. It is Penicillium or Penicillum 

 — a "■ painting brush," from whence we derive the word pencil, as 

 applied to an artist's brush. The tuft of spores surmounting the 

 simple stem, like the tuft of hairs in a brush inverted, is well re- 

 presented by the generic name Penicillium. In speaking of this 

 mould, therefore, we must speak of it as a Penicillium, since Asper- 

 gillus glaucus, the " blue mould" of cheese, and other substances, 

 is liable to be confounded with it if the term " blue mould" is em- 

 ployed. 



The Penicillium, and especially this species, Penicillium c?*usta- 

 ceum, is one of the most common of moulds. Most of us have 

 some knowledge of a curious, interesting-looking production which 

 is called a "vinegar plant," something like a piece of dirty, 



