266 
Journal of Agricultural Research 
Vol. II, No. 4 
writer that all strains belonging to the section Elegans agreed closely 
enough to justify their determination as varieties of Fusarium vasin- 
fectum Atkinson. At the height of growth, however, the conidia differed 
in the finer form, the size, septation, and in color shades. The produc¬ 
tion of sporodochia and pionnotes, the color of mycelium, and such 
functions as the pathogenicity offered other determinative factors. Sec¬ 
ondary characters, such as the production of odors on steamed rice, 
wheat, and com, also aided the differentiaton. Two species, their sub¬ 
cultures and reisolations, are proved to be xylem parasites by Harter 
and Field. These species produced wilt disease, while others refused 
to do so. The latter agreed in morphology either with F. oxysporum or 
with F. orthoceras , the former differed and have been described as F. 
batatatis and F. hyper oxysporum. The differences illustrated in Plate 
XVI, figs. D and F, and described in the diagnosis are striking to the 
writer, but he knows that there is one weak point which allows criticism 
of his opinion. He was unsuccessful for two years in the attempt to 
transform one of these fungi into the other. However, it is of funda¬ 
mental value and of vital importance in the classification to find out 
whether these conclusions are right or wrong, and strains of the various 
fungi of this section will be available to anyone who may care to throw 
further light on the complicated problem of drawing the border line 
between species, subspecies, varieties, and subvarieties, or proving that 
border lines do not exist to the extent claimed in this paper. 
It seems at first probable that there is only one fungus causing the same 
disease on one host, but okra {Hibiscus esculentus) and eggplant (Solanum 
melongena ) are attacked by Verticillium in one district and by Fusarium in 
another district, although the wilt symptoms are so similar that isolation 
and study of the parasite are the only means of deciding which fungous 
genus is connected with the trouble in each case. Furthermore, at least 
three serious wound parasitic species of Fusarium cause potato tuber-rot. 
Here, also, the isolation of the fungus, not the general appearance of the 
tuber, decides the question which parasite does the damage. In some 
cases the climate and methods of cultivation are essential. They offer 
ideal conditions for one fungus, but not for the other. But this is not 
always so, and the zone of distribution of one fungus overlaps that of the 
others. These facts may become important for the control of disease, 
and the good results performed by an exchange of seed may not be due 
simply to climatic factors, but to the weakening of parasites by a change 
of their optimum environmental conditions. Of course, a change of 
climate may be fatal to the fungus and its host, but there is no reason why 
it should not be supposed that a zone exists where the host thrives well 
and the parasite degenerates. Often, however, if one parasite has been 
successfully controlled, there will soon be another. Control methods may 
be greatly aided by a careful study of the parasites. In finding what is 
