I68 
BASCOMBE BRITT HIGGINS 
The only common wild species in this region which may harbor 
the fungus which attacks the sweet and sour cherries is P. pennsyl- 
vanica. 
There appears to be no danger of the disease passing from the wild 
choke cherry or the wild black cherry (P. serotina) to the sweet or sour 
cherry; but the fungus from the former may infect nursery seedlings 
of P. mahaleb. 
The fungus on the plums has so far been found to infect nothing 
but plums, but some of the wild plums, certainly P. americana, may 
harbor the fungus. 
Conclusions 
1. There are at least three species of Cylindrosporium parasitic 
on species of the genus Prunus, which in their conidial stage resemble 
each other very closely. Whether or not Cylindrosporium padi Karst. 
also occurs in North America is not known; but from the fact that it 
occurs on P. padus, which has racemose flower clusters similar to P. 
serotina and P. virginiana, it is perhaps the same as that occurring on 
the two last named species. 
2. The conidial stroma of Cylindrosporium on Prunus develops 
centrifugally and is never turned up at the edges so as to resemble a 
pycnidial structure. 
3. The mycelium of the species of Cylindrosporium studied is 
intercellular and obtains its food, in part at least, by means of haus- 
toria which penetrate the host cells. Very often a cellulose sheath is 
then deposited around the haustorium by the host protoplasm. It 
seems that no toxin or substance injurious to the host protoplasm is 
secreted by the fungus, but a few of the host cells are killed probably 
by drying. 
4. "Shot hole" formation in the leaves of the host is apparently 
correlated with the presence of amygdalin. The amygdalin molecule 
breaks down into simpler molecules thereby probably increasing the 
osmotic pressure which causes the cells surrounding the spot to enlarge 
forming the separation layer. 
5. Beside the Cylindrosporium conidia three other spore forms 
are found in the life cycle of the species studied, viz.: microconidia 
(spermatia-like bodies), ascospores, and apothecial conidia. All of 
these except the microconidia are known to propagate the fungus on 
living leaves. 
