July is, 1914 
Fusarium on Sweet Potato 
267 
normal, abnormalities and conditions which lead to them may be deter¬ 
mined. Abnormalities of one fungus, unfortunately, may resemble the 
norm of another. Without studying the criteria of the norm, two fungi 
may be mistaken for one. Literature shows that this error leads to more 
trouble than the mistake of drawing too sharp a border line between 
closely related species. 
Fusarium batatatis differs from F. hyperoxysporum. The conidia of the 
former are 11 to 13 times longer than broad (PI. XVI, fig. D) t while those 
of the latter are 8 to 9 times longer than broad (PI. XVI, fig. F). The 
apical cell is slender in the former, while bottle-shaped in the latter. 
The base of the latter is more pronouncedly pedicellate than in F. batatatis . 
The microconidial stage prevails in F. batatatis , giving the pure culture on 
steamed potato tuber a powdery appearance. However, a few of the 
larger septate sickle-shaped conidia will be found scattered among 
microconidia. These macroconidia (Pi. XVI, fig. D), repeatedly selected, 
and cultured separately, will result in the reduction of the microconidia 
and the aerial mycelium to a minimum, so that a perfect pionnotes 
(PI. XII, fig. B) can be produced on the very same substratum. This 
pionnotes produces abundant chlamydospores (PI. XVI, fig. B) and 
redevelops microconidia in old age (PI. XVI, fig. C), which look like a 
parasitic growth on the spore slime of the former. There is no difficulty 
in favoring the production of a particular stage, and one stage can easily 
be transformed into the other, but the constant tendency to form micro¬ 
conidia is characteristic of this fungus. In order to study the stroma, 
transfers of mycelium or microconidia were made to potato cylinders. 
The fungus rapidly formed a thallus-like layer (stroma) covering the 
surface of the substratum. When the potato was sufficiently decom¬ 
posed and its water consumed by the fungus, the stroma became shriveled. 
Blue blisters of sclerotial structure smaller than a pinhead appeared at 
this time by hundreds within the stromatic layer. These sclerotial 
bodies (PI. XII, fig. A) correspond to the stroma of sporodochia as proved 
in parallel cultures on steamed stems of sweet potato, potato, or sweet 
clover. They develop within the epidermis of the stems and often 
push through in order to develop a convex layer of the sickle-shaped 
macroconidia. The stromatic thallus on potato tuber is unnecessary 
for the fungus on stems, and is replaced by endodermatic hyphae which 
develop the sclerotial base of the sporodochia described. The blue bodies 
having a plectenchymatic structure may be called sclerotial plectenchy- 
mata. If they are spherical, as in F. sclerotium y the writer has called 
them sclerotia, and there is reason enough for not drawing too sharp 
a distinction between these different types. 
The blue color turns red with acids, and a wine color on steamed rice 
(PI. XII, fig. C) which turns blue with alkali shows the reverse effect of 
the reaction the fungi produce when grown on different media. 
4753 *14 -2 
