188 
B. B. Higgins, 
to elliptical, two to five millimeters in diameter, and often coalescing until 
the entire leaf was killed and dropped from the tree. Each spot bore 
many fruit bodies in contrast to the solitary fruit body in Cylindrosporium. 
“Shot hole" was often produced in early summer. When this occurred a 
separation layer formed outside the dead area and the spot dropped out. 
When sectioned the fruit bodies were found to have a distinct pyc- 
nidial wall with a rather large pore at the apex. They were small, glo¬ 
bose to elliptical, and entirely embedded in the tissue of the leaf barely 
breaking the epidermis on either surface, but most commonly on the upper 
surface. 
These observations left little doubt of the relation of the fungus to 
the form genus Septoria. Since, however, some confusion has arisen as 
to the limits of Septoria and Cylindrosporium 1 ) a comparison of its 
development and life history with that of Cylindrosporium was thought 
desirable. 
For the purpose of studying the fruit bodies a number of the spots 
which were beginning to assume the scalded appearance were killed, and 
embedded in paraffin. When sectioned and stained this material showed 
pycnidia in many primary stages of development. 
The development of the pycnidium is very similar to that described 
for Diplodia by Bauke 2 ) and called by Zopf 3 ) “Knäuelfrucht." It 
usually begins just beneath the epidermis, more rarely within the epider¬ 
mal cell or even deep in the palisade layer. A mycelial thread becomes 
profusely branched, the branches forming a small, round, and rather com¬ 
pact knot (figs. 3, 4). The knot enlarges rapidly and pushes down into 
the deeper leaf tissues. At the same time the branches which make up the 
knot coalesce and form an oval or globose hollow structure which is open 
at the top. At maturity the wall of the pycnidium is pseudoparenchy- 
matous but very delicate. The conidiophores arise as short branches from 
the inner surface of the wall. The development is therefore “angiocarpous" 
while that of Cylindrosporium is “gymnocarpous". 
Another important character in which this fungus differs from 
Cylindrosporium is found in the relation of the mycelium to the host 
tissue. Instead of being intercellular as in that genus, it passes directly 
through the host cells. When the end of a thread comes in contact with 
a host cell a small hole is apparently dissolved through the wall and the 
thread becoming much constricted passes through and enlarges again on 
the other side (fig. 1). 
The diseased trees were growing in a small thicket made up almost 
entirely of this species with a few small trees of. Prunus sèrotina, which, 
however, were not affected by the fungus. The infection became very 
severe toward the end of summer, so that there were very few leaves 
1) A very similar if not idential fungus on leaves of Prunus pennsylvanica was 
distributed in Fungi Columbiani (Nr. 3316) as Cylindrospornim Padi-cerasina Peck 
n. v. So far as I have been able to find, however, no description has ever been 
published. The pycnidia and spores as well as the effects on the leaf tissue are very 
similar to those of the fungus under consideration. 
2) Bauke, H., Beiträge zur Kenntnis der Pycniden, 1 (Nova Acta, K. 
Leop. Carol. Deutschen Akad. Naturf. 38, with 6 plates; Dresden 1876). See Just’s 
Jahresb. 4, p. 176, 176, 1878. 
3) Zopf, W., Die Pilze, p. 60, 1890. 
