68 College of Forestry 
and became more regular and constant in its growth as it 
grew older. Such a physiological response of the mycelium 
is not phenomenal, since the mycelium of the fungi in gen- 
eral must necessarily be very plastic and susceptible to re- 
sponse in order to more nearly bring it into harmony with 
the extremely varied conditions under which it must grow. 
In those hanging drop cultures in which the growth of the 
mycelium seemed to have come to a standstill, due probably 
to lack of sufficient nutriment for further growth, it was 
noticed that the mycelium invariably became strongly vacuo- 
late. In hanging drop cultures of basidiospores grown in 
sugar-wood decoction it was observed that the mycelium, after 
two weeks’ growth, began to break up into oidia. 
The germ tubes develop rapidly into an extensive primary 
mycelium characterized by the total absence of clamp con- 
nections and the rare occurrence of cross-walls. In thriving 
cultures the mycelium branches profusely soon after the 
germination of the spore. After five or six days’ the hyphz 
of the primary mycelium give off branches which differ from 
those of the primary mycelium 3 in that they possess abundant 
clamp connections and cross-walls. These hyphe constitute 
the secondary or mature mycelium which at first grows inter- 
mingled with the primary mycelium and sometimes anasto- 
moses with it. The latter, however, soon loses its contents 
and disappears from the culture. This change in the myce- 
lium oceurs regularly in all cultures, both thigenta hanging 
drops and those on agar plates, and apparently is not influ- 
enced by the nature of the culture medium or by other 
external conditions. 
The germination of the spores and the method of growth 
of the mycelium is illustrated by camera lucida drawings on 
Plates VIII and 1X. In connection with each of these plates 
the age of each germinated spore is indicated approximately. 
The size attained by the mycelium varies greatly according 
to the suitability of the culture medium used and the con- 
ditions for growth. In general the drawings represent the 
% Usually longer in hanging drop cultures. 
