Apr. as. 19*3 Species of Fiisarium Isolated from Potato Tubers 
343 
importance of different characters, defined certain forms of fructification, 
reviewed the genus Fusarium, and explained the difficulties of identifying 
species of Fusarium with previously described species because of the 
scarcity of taxonomic detail in the descriptions. The greater part of the 
memoir is taken up by the description of sections, genera, species, and 
varieties. He listed 20 previously described species, including parasitic 
and nonparasitic forms—all that were known to occur on potatoes—^and 
41 new species and varieties. These 61 forms he distributed under 
Wollenweber’s eight sections and three additional ones that he himself 
originated and defined. Three species of Ramularia, a genus closely 
related to Fusarium and also occurring on potatoes, are included. There 
are drawings of practically all species and varieties, showing conidia, 
conidiophores, and occasionally mycelium. Spore measurements are 
given for spores grown on various culture media. 
Based on the ideas of Appel and Wollenweber, Sherbakoff {18) worked 
out a dichotomous key for the species of Fusarium described, which, 
while the best yet published, is far from perfect. Imperfections in keys 
are rather inevitable until methods used in the identification of the 
species are better standardized. Until standard methods are adopted, 
the boundaries of species can not be closely enough defined to prevent 
investigators from introducing numerous varieties, separating one from 
another on minor characters that are not stable under all conditions. 
In the key, Sherbakoff uses septations and shape of conidia most often 
as differential characters. Presence or absence of microconidia, chlamy- 
dospores, sclerotia, sporodochia, type of fructification, and color and t3^e 
of conidiophores are also used. Difficulty with the key arises most often 
in the case of varieties. Individual difficulties of this sort will be noted 
later. Confusion often arises from the misuse of the terms macro- 
conidia and microconidia, but this may be due to t3T)ographical errors. 
C. W. Carpenter (4), in a paper on tuber-rots caused by species of Fusa¬ 
rium, includes a section on taxonomy which gives the description of eight 
species. Among these one is new, F. eumartiiy which falls into the sec¬ 
tion Marteilla. 
Link {13) shows some very interesting results from physiological 
studies on Fusarium oxysporum Schlect and F. trichothecioides Wr. 
Comparisons of the two species are given to show temperature rela¬ 
tions, growth, habit, and food requirements and pathogenicity to tubers 
and growing plants. 
Pratt (75), in a paper on control of powdery diyrot caused by 
Fusarium trichothecioides Wr., concludes that this species is of the high¬ 
est economic importance of all of the Fusarium species in the irrigated 
portion of the West, and in another paper {14) notes that F. radicicola 
Wr. is rather common in desert soils. 
Hawkins (<?), in stud3dng the effect of certain species of Fusarium on 
the composition of the potato tuber, found that Fusarium oxysporum 
and F. radicicola secrete sucrass, maltase, xylase, and diastase. The 
last-mentioned enzym is apparently incapable of acting on the ungela¬ 
tinized potato starch. The purpose of the study was to find out what 
constituents of the potato are most easily destroyed by the fungus and 
what compounds can not be utilized by it either in respiration or in 
building its own tissues. Their results are not condusive as to whether 
kind or quantity of secretion is in the least specific, as only three organ¬ 
isms were used in their experiments, but this artide introduces an 
interesting phase of the Fusarium problem. 
