May 10,1924 
Physalospora malorum on Currant 
587 
is due to differences in the physical character of the bark or to the chemical com¬ 
position of the food the twigs supply to the fungus must remain for further inves¬ 
tigation. 
That the change in amount of stromatic tissue and in arrangement of spore 
cavities is in fact due to the host is further indicated by the behavior of the 
closely related Diplodia natalensis Pole-Evans, which causes a serious rot of 
citrus fruits in Florida. 
Plate 2, B, C, and D, show sections of mature pycnidia of Diplodia natalensis 
grown on sterile twigs of apple and currant from single spore cultures from grape¬ 
fruit. It will be noted that on apple twigs the pycnidia are usually separate even 
when near together, whereas on currant twigs they tend to aggregate. The differ¬ 
ence here must be due to the difference in substratum, since the cultures were all 
made at the same time by transfers from a single spore culture and during their 
growth on twigs were kept together in flasks on the same bench in a greenhouse 
for the same length of time. This would seem to indicate that in these fungi the 
size of the sporocarps and the amount of stromatic tissue associated with a single 
spore cavity is not a constant character. 
SUMMARY 
The perfect stage of the Sphaeropsis common on dead currant canes has been 
demonstrated to be a Physalospora, which is apparently identical with P. 
malorurriy the fungus causing blackrot of apples. The chief difference in the 
appearance of the fungus on the two hosts is in the size of the sporocarps, which 
on currant are large and usually contain several spore cavities, while on apple the 
sporocarps are much smaller and usually contain only one spore cavity. This 
difference in the size of the sporocarp is apparently due to the difference in the 
substratum. Pycnidia produced on sterile apple twigs from pure cultures of the 
currant fungus are small, while those produced on sterile currant twigs from pure 
cultures of the apple fungus are large and usually contain several spore cavities. 
A similar difference in the size of the sporocarps is found when pycnidia of 
Diplodia natalensis are produced in pure cultures on sterile twigs of apple and 
currant. 
