10 BULLETIN" 64. U. S. DEPARTMENT OP AGRICULTURE. 
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 
d imin ished 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 wilt 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 WDLT. 
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 of the northern border, where wilt is, at least, 
uncommon. Most of the Fusarium wilt 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. sulpliw- 
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 role in these early crops, but has been found in the 
second or fall crop. 
As already 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 
