534 PATHOGENIC FUNGI 



germinate to produce a new mycelium. In rich culture media or old 

 cultures the mycelium may become septate. Cultivated under water 

 some species (including Ohlamydomucor racemosus) enter into an oidial 

 .condition. 



Ascomycetes : (1) Aspergillus herbariorum (=A. niger). — This, with 

 other varieties of the same group, is of frequent occurrence, especially on 

 dead vegetable matter. It grows readily on gelatin and, to' the naked 

 eye, consists of a mass of filaments which microscopically are seen to 

 form a septate branching mycelium. Two forms of reproduction occur, 

 the variety depending largely on the nutrition of the plant. The less 

 common form is effected by means of structures known as ascocarps, which 

 owe their formation to a sexual process. From a mycelial branch there 

 arises a hypha which becomes specially coiled and transversely septate at 

 its end. From the base of the lowest coil of the spiral two or three 

 hyphae grow up towards its apex, where one of these fuses with the coiled 

 hypha and represents the male organ. The others by branching 

 copiously produce a mass of closely woven hyphse forming a closed wall 

 to this structure, which is the ascocarp referred to. Within it numerous 

 asci arise as the ultimate ramifications of branches given off by the 

 central coiled hypha. Inside each ascus eight ascospores are produced. 

 Ultimately all the structures lying within the ascocarps, save the spores, 

 undergo disintegration, so that the mature ascocarp consists of a small 

 hollow sphere within which lie the loose spores. These latter are ulti- 

 mately freed by the decay of the wall of the ascocarp and develop into new 

 individuals. The commonest method of reproduction is by the formation 

 of spores in the form of conidia, which are clearly of non-sexual origin. 

 A filament grows out, and at its termination a rounded swelling is formed 

 on which a series of little finger-like processes called sterigmata are 

 perched. At the free end of each of these, rows of oval conidia are suc- 

 cessively abstricted. Each conidium, on becoming free, can give rise to 

 a new individual, just as can an ascospore. 



(2) Penicillium crustaceum (=Penicillium glaucum). — This is 

 perhaps a composite species and is the most common of all fungi met 

 with in bacteriological work. It is the common green cheese mould, and 

 its extraordinary versatility and powers of resistance make its spores 

 practically omnipresent. The mycelium is like that of the Aspergillus. 

 Ascocarp formation takes place, but the commonest mode of reproduction 

 is by the conidia. A filament (the conidiophore) grows out, and at its 

 end frays out into a pencil of finger-like branches. On the point of each 

 of these a peg-like sterigma is developed. On the end of this a row of 

 oval conidia is successively cut off ; these break off and can give rise to 

 new individuals. 



(3) Saccharomyces or Yeasts (Torula, Mycodenna). — These organisms 

 have been subjected to much investigation in consequence of their 

 economic importance in brewing and baking. They occur in nature 

 chiefly in connection with fruits, such as the grape, which contain 

 fermentable sugars. They consist of round or oval cells, 3 to 5 /u in 

 longest diameter, and under ordinary conditions reproduce themselves by 

 budding, in which process a portion of the cell protrudes, increases in 

 size, and finally becomes separated from the parent cell so as to form a 

 new individual. In a number of other fungi belonging to the various 

 groups, the conidium, when cultivated in a liquid, has the power of 

 budding off conidia which behave in like manner ; such fungi, therefore, 

 have a yeast-like stage in their life-history. Under certain Conditions of 



