Heterosporium asperatum. By Mr. G. Massee. 583 
The numerous failures recorded in attempting to corroborate 
statements in connection with the inoculation of certain species of 
plants with a particular fungus, appear to indicate that this immunity 
from disease is not an uncommon feature in plant life. 
The above remarks naturally suggest the question, What are the 
causes that give to certain individuals immunity from a specific 
disease ? On the solution of this problem would appear to depend 
the successful issue of the much desired knowledge that would enable 
us to protect plants from the wholesale destruction caused by fungi. 
It is certain that we cannot eradicate noxious parasitic fungi; 
the present preventive method of combating these pests, although 
useful to some extent, does not suggest finality ; and notwithstanding 
the amount of research connected with the life-history of parasitic 
fungi, it must be admitted that the general principles of an exact 
method of dealing with the subject from a practical point of view, 
remain to be discovered. 
To return to the fungus under consideration. During the summer 
the isolated patches of disease that correspond to independent centres 
of infection, increase in size and run into each other, the whole 
leaf not unfrequently presenting a blackened appearance, caused by 
the dark-coloured hyphae. 
During the autumn the stronger branches of the vegetative hyphrn 
increase considerably in thickness, many of the cells becoming very 
much inflated and spherical and separated by deep constrictions, due 
to the transverse septa not increasing in diameter. Many of these 
stout hyphse become more or less irregularly branched and contorted 
at the tip, the convolutions approach each other, and by repeated cell- 
formation produce a more or less globose sclerotium-like body, almost 
black externally, somewhat paler inside (fig. 11). These sclerotia are 
of small size, rarely reaching 1 mm. in diameter, and remain passive 
during the winter. In the following spring certain of the external 
cells of the sclerotia become more prominent than the rest, and 
eventually grow out in a radiate manner from the sclerotium as 
slender, colourless, septate hyphae or sporophores, each producing at 
its apex a whorl of simple or branched concatenate chains of small, 
elliptical, olive spores that agree in every particular with the 
secondary spores borne on the mycelium of the germinating spores 
(fig. 12). The spores produced by the sclerotia, when placed on the 
leaves of the host-plant, produce the Heterosporium. 
Fig. 6 represents two sporophores of the Heterosporium after 
remaining in water on a slide for four days ; it will be observed that 
two slender filaments have developed, each bearing a fascicle of chains 
of spores similar to the secondary spores borne on the filaments of 
germinating spores. 
Finally, if leaves infested with the Heterosporium are examined 
in the autumn, minute, blackish perithecia will in many instances be 
