M. C COOKE ON BLACK MOULDS. 257 



Fungi we have the genus Sporidesmium, to which some of the so- 

 called species of Stemphylium belong. It might prove a puzzling 

 occupation, and in some sense a suggestive one, to compare together 

 the structure of all the genera of black moulds with these peculiar 

 compound spores. 



In the Handbook, unfortunately, by some error which I cannot 

 now account for, the figure 248, supposed to represent Mystrospo- 

 rinm belongs to a distinct genus, that of Blastotrichum. 



In Septosporium, if the original features of the genus are main- 

 tained, there should be threads resembling a Helminthosporium, with 

 septate spores attached to a short pedicel, and usually generated at 

 the base of the threads. It bears about the same relation to Hel- 

 minthosporiam which Macrosporium does to Cladnsporium. Two or 

 three species have been found in this country, and I have described 

 a very distinct one from the United States, in which the typical 

 character is maintained, and in these instances there is a good cha- 

 racter to separate them from the genus Macrosporium. 



As far as I can offer any one feature to distinguish the three 

 British genera so closely allied, I should suggest that the spores of 

 Mystrosporium are terminal, those of Septosporium basal, and those 

 of Macrosporium are scattered. Moreover the spores of Mystro- 

 sporium and Septosporium are dark and opaque, whilst those of 

 Macrosporium are translucent. 



It is by no means satisfactory to define the limits of any one 

 genus by a single character. This is a great mistake, into which 

 young and inexperienced naturalists are apt to fall. It is by general 

 resemblances into which all features of the individual enter that 

 affinities are to be determined. By a comparison of all the salient 

 features, judgment must be pronounced in favour of the greatest 

 amount of agreement. A sound classification must be natural, and 

 not artificial. It seems strange that there should be any necessity 

 for urging this truism, which has long since been accepted, and yet 

 all our modern " improvements" in classification show a tendency, 

 not to advance, but to retrograde into an artificial system which our 

 forefathers discarded as insufficient. 



Succeeding the Macrosporiuid group, it may be well to allude to a 

 group of peculiar interest to those of our younger microscopical 

 friends who are in search of curious or pretty objects This is the 

 group with Helicoid spores, and here, I fear, that I must again 

 trouble you with a few technical observations in order to clear the 



