M. C. COOKE ON MICROSCOPIC MOULDS. 65 



the structure of the stem, we have a decided generic difference 

 between these species of Artlirobotryum, and those of the other 

 genera alluded to. 



The dead stems of such umbelliferous plants as the common Hog- 

 weed, Angelica, &c, also nourish Black Moulds, and one of these 

 may be taken as the type of another genus. I allude to Den- 

 dry phium fumosum, figured by Corda under the name of Dactylium 

 fumosum. The branched threads in this species (Plate v.) are sur- 

 mounted by large and beautiful elongated fusiform brown spores, 

 which are transversely divided by numerous septa. One peculiarity 

 in their mode of growth is that the spores are produced in chains ; 

 that is, one spore supports another at its apex. This concatenate 

 condition of the spores is not always readily made out, because 

 the attachment is so slight that unless great care be exercised, only 

 single spores will be found attached to the threads. In some 

 other species the attachment is more permanent. 



By comparing together the examples I have given of the 

 Dematiei, the general features of the order will be readily appre- 

 hended. The threads are free, or sometimes collected together so 

 as to form a compound stem. They are also more or less fur- 

 nished with an outer membrane, which may often be seen peel- 

 ing off in the flocci of Helminthosporium, and have a burnt or 

 charred apj>earance, never white or of pure tints, as in the 

 Miicedines, and the spores have frequently the same carbonized or 

 brown tint. The distinctions between these orders are, I think, 

 manifest in the characters I have given. 



These are the two largest orders in the family to which they 

 belong, but there are four others, each containing a few genera, to 

 which I must allude. A few years since our worthy secretary, at 

 that time, called my attention to some cat's clung which was found 

 in one of his cellars. It was covered with a curious-looking 

 mouldy substance, but there were no heads, and the thick snow- 

 white coralline threads had a peculiar powdery appearance. When 

 examined under the microscope, these threads, or branching stems, 

 were found to be composed of a mass of delicate hyaline threads, 

 bearing a profusion of powdery minute spores at the surface. It 

 was Isaria felina, found for the first time in Britain. A similar 

 structure prevails through the order to which this species belongs. 

 The common stem is compound, and the powdery spores are borne 

 on the surface, giving the fungus a peculiar pulverulent appear- 



