75 
NOTE ON A MINNESOTA SPECIES OF ISARIA AND AN ATTENDANT 
PACHYBASIUM. 
By Conway Mac Millan. 
Early in April Mr. E. P. Sheldon found on the river bank below St. 
Anthony’s Falls, Minn., a pupa of Orgyia leucostigma, commonly known 
as the Tussock moth, which was covered with a growth of Isaria. The 
fungus does not correspond to any described species in all its charac¬ 
teristics, though I have determined it provisionally as Isaria sphingum , 
Sehw., which is the conidial form of Cordyceps sphingum , (Tul.). The 
description of the Minnesota form is appended : 
Stromata gregarious; 1J to 3 centimeters high, \ millimeter thick, and 
slightly subclavate, arising from a pulverulent-granulose, yellowish 
mycelium, conidial area but slightly thickened, hyphae kp in thickness, 
indistinctly yellowish, conidia very minute, ovoid, 1J-2 by £-1 \p^ 
hyaline, deciduous. 
This does not coincide exactly with the description of Isaria sphingum , 
Scliw., given in Saccardo’s Sylloge Fungorum , but in the genus Isaria , 
and throughout many of its allies exact descriptions are not attainable, 
owing to the failure of the older mycologists to measure hyphae and 
spores as well as stromata and conidial areas. 
An effort to cultivate this species of Isaria was made. 
Portions of conidial areas were removed with sterilized forceps, and 
were then placed, with every precaution, in gelatine culture tubes. 
Some of those, prepared by Dr. George Griibler, of Leipsig, happened 
to be at hand and were chosen for three cultures. Repeated experi¬ 
ments showed that, together with adventitious forms— Macrosporium in 
one case and Piptoceplialis in another—a very peculiar plant, clearly of 
the genus Pacliyhasium , Sacc.—was constantly developed in the gelatine 
tubes. This Pacliyhasium , distinguished by its bottle-shaped (ampulli- 
form) basidia, whorled along the fertile hyphse, as in Verticillium , 
Nees., is possibly P. hamatum , (Bon.) Sacc., described in the Sylloge Fun¬ 
gorum Yol. IV, pp. 149,150. Since, however, the Saccardian descrip¬ 
tion lacks measurements, a description is appended. 
Forming minute yellowish patches on gelatine, becoming grayish or 
greenisli-white, fertile hyphae 3i-4 p. in thickness, 40-90 p. in length; 
ascending with whorls of basidia, either directly attached or with 
secondary branches interpolated ; basidia shortly ampulliform, necks 
constricted, conidia ovoid 1J-2 by £-lJ /*., clinging persistently to the 
basidia. 
It will be seen that measurements of the spores and hypliae of this 
Pachybasium correspond exactly with those given above for the Isaria , 
and this fact, together with the appearance of the former so uniformly 
in connection with the latter, might tend to give the impression that 
the two genera are pleomorphous and that in Pachybasium we have 
another step in the life history of Cordyceps. It is well known that 
I 
