Fusarium Blight of the Soy Bean 
25 
difference in the character of mycelium until advanced ages of 
the cultures and generally, but not always, an absence of flesh- 
colored sclerotia in the soy bean fungus. These differences, how- 
ever, are not believed to be of sufficient importance to warrant 
regarding the soy bean strain as a distinct species or variety. 
In addition to the media emj^loyed in Table 2, potato hard 
agar, cornmeal plugs, and string-bean pods were used, but they 
showed no additional characters of value. 
Perithecia have' never been observed on the diseased stems; 
neither have they been obtained in cultures from the surface spores, 
nor from the diseased internal tissues. In fact, the cultural differ- 
ences between the Fusarium sp. on soy bean and N eocosmospora 
spp. are as striking as between N eoeosmosfora spp. and the 
several species of Fusarium causing wilt studied by Higgins (14) 
and Butler (3). 
INOCULATION EXPERIMENTS 
From the foregoing morphological and cultural studies, it is 
evident that the species of Fusarium on soy bean is not distin- 
guished from F. tracheijFiilum by any well-defined differences. 
Since the i30ssibility existed that they might be separated by 
biological differences, reciprocal inoculation studies were under- 
taken to secure additional evidence of their identity.^ 
Plants were therefore grown in pots and flats in the green- 
house and in plots in the field for use in inoculations. The soil 
used in the pots and flats was a fine, compact, sandy loam, except 
in the case of one experiment, and was taken from a field in 
which diseases of cowpeas and soy beans caused by Fusarium spp. 
had iieA^er been observed. In certain of these tests, as an added 
precaution, the soil was partially sterilized by the use of a 2 per 
cent solution of formaldehyde. The seed were also sterilized in 
certain experiments by immersion for 15 minutes in commercial 
sulphuric acid. Since uninoculated plants remained free from 
disease when these precautions were not employed, their use Avas 
discontinued in subsequent tests, unless otherwise stated. 
The pots and flats were of sufficient size to permit the plants 
to grow to maturit}^ 
In determining the percentage of diseased plants, count Avas 
made only of those in Avhich it was possible to find discoloration 
and iiiA^asion of the xylem tissues. In case of doubt in this micro- 
scopic examination, planted plates were made from the tissues and 
the subsequent growths studied. 
The A^arieties of soy beans and coAvpeas planted for the cross- 
inoculation experiments were Imown to be subject in the field to 
the species of Fusarium on soy bean and cowpea, respectiA^ely. 
UVollenweber (31, p. 37) says that a consideration of the biological characters is of 
secondary importance in the determination of species. 
