July is, 1914 
Fusarium on Sweet Potato 
257 
some the illustration and description gave complete data. The most 
questionable method, however, was to base identification of a fungus on 
exsiccatse alone. Dried specimens often contain stages collected from a 
moist location, drying out later, causing constrictions and other changes 
in the general shape and curvature of the spore so that even the col¬ 
lector would not always recognize his own specimens if he did not know 
the cause of these changes. The cross walls or septa of the spores in 
overwatered cultures are frequently absorbed, a condition often con¬ 
sidered as normal in old genera and many species of Fusarium. It is not 
known whether species with long sickle-shaped conidia of the unicellular 
type exist in this genus, but it is evidently not the rule. Unicellular 
normal spores of the small ellipsoidal stage, however, exist in all species 
of Fusarium and form a normal stage in some sections, such as Elegans. 
These unicellular spores aid in the rapid distribution of a disease. In 
other sections, such as Discolor and Roseum, the unicellular type is 
normal in particular species, but subnormal in most others. This fact 
shows that exsiccated specimens of Fusarium containing a mixture of all 
types of conidia do not allow an exact determination when they are 
collected from nature. 
I. FUSARIUM Link 
A. SECTION MARTIELLA 1 
[Species in section Martiella are Fusarium solani (Mart.) Sacc., F. martii App. and Wollenw., F. 
coeruleum (Lib.) Sacc., and F. radicicola , n. sp.] 
Fusarium radicicola, n. sp. 
Diagnosis.—Conidia, normally 3-septate, may occur scattered in sporodochia or 
pionnotes, averaging 30 to 45 by 3.75 to 571; 25 per cent of the total number may be 
4-septate; 5 per cent may be 5-septate and average 40 to 59 by 4 to 5.25//. Chlamy- 
dospores, 7 to top, agree with those of other species of the section Martiella. 
Habitat.—On partly decayed tubers and roots of plants, such as Solanum tuberosum 
in Europe and America (collected by Wollenweber) and Ipomoea batatas in the United 
States of America (collected by Harter and Field). 
Fusarium radicicola (PI. XVI, fig. K) has the characters of the sec¬ 
tion Martiella. The conidia are narrower than in Fusarium solani 
(Mart.) Sacc. (sensu strict.), which has 3-septate conidia averaging 
30 to 40 by 5 to 6j a in size and are shorter and have fewer septa- 
tions than in F . martii App. and Wollenw., which has 3- to 4-septate 
conidia averaging 44 to 60 by 4.75 to 5.50// in size. The plectenchy- 
matic mycelium is olive colored on sterilized potato tuber, with all 
shades from green to brown. The description has been made from a 
strain isolated from an Irish potato tuber grown in 1912 on the Potomac 
Flats, near Washington, D. C. 
Fusarium radicicola resembles slightly the conidial stage of Hypomyces 
cancri (Rutg.), n. comb. (PI. XIII, fig. /), but has no pedicellate base 
1 The author established these sections (Wollenweber, 1913c) with the diagnoses of the species and ref¬ 
erences to complete previous descriptions (Appel and Wollenweber, 1910). 
