206 
Journal of Agricultural Research 
Vol. V, No. $ 
Habitat.—On partly decayed tubers and roots of plants. Cause of potato dry-rot 
and jelly-end rot. Identified from the following: Ipomoea batatas (collected by 
Mr. L. L- Harter); Musa sapienium (collected by Mr. S. F. Ashby, Jamaica, Porto 
Rico); Cucumis sativus (collected by Mr. F. V. Rand, West Haven, Conn.); soil 
(collected by Mr. F, C. Werkenthin, Austin, Tex.). 
B. SECTION ELEGANS 
[Species in this section are F. oxysporum Schlecht., F. hyperoxysporum Wollenw., F. vasinfectum Atk., 
F. tracheiphilum Sm., F. niveum Sm., F. lycopersici Sacc., F, conglutinans Wollenw., F. redolens Wol¬ 
lenw., F. orthoceras App. and Wollenw.. F. orihoceras, var. triseptatum Wollenw., F. batatatis Wollenw.] 
1. Fusarium oxysporum Schlecht. (20, p. 28). 
2. Fusarium hyperoxysporum Wollenw. (21, p. 268). 
F. oxysporum (PI. XIV, fig. 1) is not sharply differentiated morphologically from 
several species of this section—namely, F. hyperoxysporum, F. vasinfectum, F. trachei¬ 
philum , F. lycopersici , and F. niveum. F. hyperoxysporum forms a perfect pionnotes 
in contrast to the reduced pionnotes in F. oxysporum (PI. A, fig. 1-5). According to 
Harter and Field (4, p. 296), it is different biologically in that it causes a stem-rot of 
Ipomoea batatas and is not infectious on young plants of Solanum tuberosum , while 
F. oxysporum causes a wilt of the latter host but does not attack the former (21, p. 268). 
Both develop a lilac odor on starchy media. However, this character is of doubtful 
specific value since non-odor-forming strains of F. oxysporum , F. hyperoxysporum , and 
F. vasinfectum have been isolated, and some of the odor-forming strains temporarily 
lose this property in culture. 
F. tracheiphilum , the cause of a wilt of species of Vigna, is without pionnotes and 
odor. F. vasinfectum , the cause of a wilt of cotton, develops a perfect pionnotes of an 
ocherous-salmon color; on potato cylinders in subdued light this color becomes slightly 
purple. Typically a strong lilac odor is present on starchy media. A non-odor¬ 
forming strain was designated F. vasinfectum , var. inodoratum, by Wollenweber (20, 
p. 29). F. lycopersici , the cause of a wilt of Solanum lycopersicum, differs from F. 
oxysporum in having conidia of a little larger average size and produces colorless 
sclerotial plectenchymatic masses in contrast to the bluish masses of this sort in 
F. oxysporum , etc. No odor is developed. F. niveum , to which the wilt of species of 
Citrullus is attributed, differs from F. lycopersici in forming blue sclerotial bodies on 
potato cylinders; from F. oxysporum in having larger conidia and no odor. 
It is possible to determine the six above-mentioned species by morphological 
characters alone. Although a knowledge of the host of the particular species to be 
determined is not necessary, such information greatly facilitates the work. In spite 
of the fact that each of these forms seems to cause a wilt on one particular host, it 
should be pointed out that too much dependence on the value of the host in descrip¬ 
tions of species has led to the present confusion in the nomenclature of the form genus 
Fusarium. 
A species of Fusarium causing a field soft-rot of Irish potatoes in Mississippi (Pl. 
XV, fig. 1,2) was morphologically identical with F. oxysporum (PI. XIV, fig. 1), but 
developed a perfect pionnotes on potato cylinders (PI. A, fig. 4); thus, it must be 
identical with F. hyperoxysporum , the cause of stem-rot of the sweet potato. Inocu¬ 
lation with F. hyperoxysporum isolated by Harter and Field from the latter host re¬ 
sulted in complete destruction of the tubers (see No. 3399 and reisolation of same, No. 
3489, p. 192), indicating the truth of the hypothesis. 
Further cross-inoculation work carefully controlled by morphological 
studies should demonstrate whether all of the above-mentioned species 
of this section are biologically distinct; whether, for example, F. hyper¬ 
oxysporum differs sufficiently from F. oxysporum , on the one hand, and 
F. vasinfectum t on the other, to be entitled to the rank of species. 
