FusARiA OF Potatoes 113 



— is after all sufficiently stable to be used safely in a morphological 

 treatment. Even the size of conidia, when a sufficient number of measure- 

 ments is made and averaged and when only conidia of the same type are 

 compared, is of rather surprising uniformity and stability. It is believed 

 that every one will agree with these statements after an examination of 

 the data presented here in the descriptions of species. 



That Fusaria can be separated on a strictly morphological basis was 

 first definitely demonstrated by Appel and Wollenweber. 



RELATIVE TAXONOMIC IMPORTANCE OF DIFFERENT CHARACTERS 



Usually the particular organism and the prominence and stabihty of 

 a given character determines the relative importance of characters in 

 classification. Thus, in certain cases septation of conidia may be con- 

 sidered as the important character. For instance, in the case of F. dimerum 

 and F. affine, this character distinguishes these two fungi at once from 

 all the other Fusaria, while in most other cases it is not of such importance. 

 Presence of a continuous slimy layer of spores is the important character 

 in the case of F. udum var. Solani where this type of fructification is 

 especially prominent. Type of microconidia, when they are of typical 

 occurrence and especially when they are of a peculiar type, as in the case 

 of F. sporotrichioides, is also a most important character. Type of 

 chlamydospores is an important character in general for dividing the 

 whole genus into sections, but it usually has no specific value; and yet 

 there is a fungus, F. cuneiforme, which can be set off from all the rest 

 because of its terminal unicellular chlamydospores. Color may vary 

 considerably, but on the whole its type is stable enough to be of con- 

 siderable help in dividing Fusaria into sections, and sharp contrasts in 

 color can often be used for specific differentiation. 



In general the most useful and evidently sure basis for a natural classi- 

 fication of this group is the shape of the macroconidia.^^ Their clorsi- 

 ventrality, the form of their apex and their basal cell, and their septation, 

 and also their size, when properly used, are of considerable service in separa- 

 tion of species. The actual working value of each character can be seen 

 from the keys. 



28 Appel and Wollenweber (1910 : 34) and Wollenweber (1913 a : 26) came to this conclusion long before 

 the writer, gee also Lewis (1913 : 225). 



