ii6 Transactions British Mycological Society. 



and the growths compared with one another and with that of 

 V. albo-atrum on the same media. 



In their conidial form all three species are much alike, so 

 far as their aerial parts are concerned. The conidiophores are 

 very similar in each case. The size of the conidia in each 

 species varies considerably, but parallel cultures on the same 

 media showed that those of V. albo-atrum were 'on the average 

 the smallest, and those of V. nubilum the largest ; while those 

 of V. nigrescens were intermediate. The measurements were 

 made on what were considered to be the predominating type of 

 conidia, omitting the extreme forms in each case. 



The most striking differences are to be found in those portions 

 of the growths which are submerged in the culture medium. 

 In all three cases this submerged growth becomes dark after 

 a time, and finally almost black. In the case of V. albo-atrum 

 this darkening, as is well known, is caused by the turning 

 black of the submerged hyphae. In V. nubilum and V. 

 nigrescens, on the other hand, it is due, not to any change in 

 the colour of the submerged mycelium, but to the production 

 of large numbers of what may be regarded as chlamydospores 

 which develop very dark, almost black, walls. 



The chlamydospores of V. nubilum are more or less spherical 

 cells hyaline at first, but soon developing thickish, dark brown 

 or black walls. They may be borne singly or in groups of up 

 to seven or so. They may be terminal but are frequently 

 intercalary in rows of three or four or more. Examples are 

 illustrated in Fig. 5, Plate IV. They are not, however, produced 

 on all media and are usually absent in those containing gelatine. 

 The mycelium on which they are formed remains visible for a 

 long time. 



The chlamydospores of V. nigrescens are considerably smaller 

 than those of V. nubilum. They may be spherical, oval or 

 somewhat pear-shaped. Generally they are single-celled, but 

 occasionally they are septate. Many of them arise in an inter- 

 calary fashion by the thickening and blackening of non- 

 contiguous cells in a hypha, and they retain, more or less, the 

 shape of such cells. Often they are laterally sessile and then 

 generally spherical. The cells of the hyphae which do not 

 become chlamydospores become rather indistinct in old cultures, 

 and the general impression is that of a row of irregular beads 

 arranged at unequal intervals along, or at the side of, a faintly 

 visible band. Examples are illustrated in Fig, 6, Plate IV. 

 They are developed in very large numbers ; and the blackening 

 of the medium produced by them is considerably more intense 

 than that caused by the two other species. 



Although the two fungi were kept continuously in culture 



