10 BULLETIN 64, U. S. DEPARTMENT OF AGEICULTUBE. 



a ''high culture." Color differences of both spores and mycelium are 

 to be noted, and for the latter purpose potato cylinders and rice are 

 excellent. 



The final result of this line of work will be a great simplification of 

 the Fusarium problem. The number of species in the genus will be 

 diminished and the parasitic forms can be identified, for the most 

 part, by their morphological characters. It has been found that the 

 genus is divisible into sections, on the basis of form of conidia and 

 other morphological characters, and that all of the wUt parasites are 

 included in the single section, Elegans. Thus far Fusarium oxyspo- 

 rum appears to be the only Fusarium causing potato wilt; and, as 

 already stated, this is not connected with the dry-rot of tubers, which 

 may be due to one or another of four or more other Fusaria. The 

 diagnosis of these tuber troubles will be treated more at length in 

 another publication. 



CLIMATIC RELATIONS AND GEOGRAPHIC DISTRIBUTION OF FUSARIUM WILT. 



Fusarium wilt is apparently a disease of warmer climates. States 

 like California and Arizona,, with high summer temperatures, and the 

 middle States, Ohio, Missouri, and Nebraska, which are near the 

 southern border of profitable main-crop potato culture, suffer much 

 more than the States vi the northern border^ where wHt is, at least, 

 uncommon. Most of the Fusarium wHt diseases of other crops are 

 southern in their range. Owing to the fact that other species of 

 Fusarium, such as Fusarium coeruleum and F. discolor var. sulpJiVr 

 reum also occur in the Northern States and have not hitherto been 

 clearly differentiated from F. oxysporum, there is some doubt as to 

 the actual range of the latter, especially in New York and New Eng- 

 land. Going westward, the wilt fungus is found farther north, and 

 it is likely that the disease will continue to spread northward. 



In the States from New Jersey and Maryland southward to Florida 

 and westward to Texas the Irish potato is relatively a minor crop, 

 except in the trucking districts, where planting takes place in winter 

 or early spring, and the harvest for the northern markets occurs from 

 April to July, generally in advance of maturity. Fusarium has never 

 played a visible r61e in these early crops, but has been found in the 

 second or fall crop. 



As abeady stated. New England and New York are relatively free 

 from the disease. Suspected cases there have generally proved to be 

 the VerticiUium wilt. The conditions in Pennsylvania are not as 

 well known to the writer, but are probably not far different from 

 those in Ohio, where Selby and Manns have found wilt to be widely 

 distributed. The latter says : 



In this Fusarium blight we have the most persistent and destructive disease factor 

 with which the Ohio potato grower has to contend. Its subtle work in the past, though 



