JOURNAL OF AGMCDLTDRAL RESEARCH 
DEPARTMENT OF AGRICULTURE 
Voiv. V Washington, D. C., January 17, 1916 No. 16 
FACTORS INVOLVED IN THE GROWTH AND THE 
PYCNIDIUM FORMATION OF PLENODOMUS FUSCO- 
MACULANS . 1 
By George Herbert Coons, 
Research Plant Pathologist, Michigan Agricultural Experiment Station 
INTRODUCTION 
The experimentation reported in this paper was begun at the botanical 
laboratory of the University of Michigan in 1913, continued at the Mich¬ 
igan Agricultural College during the next year, and finally completed in 
1915 at the University laboratory. 
The fungus Plenodomus fuscomacidans was obtained from badly 
cankered limbs of the apple (.Mains spp.) which were sent to the Agri¬ 
cultural College laboratory in March, 1911, from Boyne City, Mich. 
Examination of the cankers at the time of receipt and field studies during 
the same month showed that the trouble was different from any of the 
described apple diseases. The cankers showed constant association with 
a pycnidium-forming fungus. This organism was obtained in pure cul¬ 
ture from a single spore, and the causal relation of the fungus to the 
canker was proved by repeated inoculations and reisolations. A study 
of the organism, both on the host and in pure culture, showed that it 
was a Phoma-like member of the large group Sphaeropsidales, and it 
corresponded to the species described by Saccardo as Aposphaeria 
fuscomaculans . 
The pycnidia, however, show morphological characters by which it is 
possible to segregate this fungus from the larger, poorly defined genus. 
These characters, which may be found in the material from the host, be¬ 
come very pronounced in culture. The pycnidia are more or less irregu¬ 
lar in shape. The fruiting layer is usually folded so that the chamber is 
recessed instead of being smooth and regular. The pycnidia are beaked. 
The wall is composed of two distinct layers and is complete, even at the 
basal portion. It seems proper to emphasize the morphological charac¬ 
ter of the wall. Accordingly, the removal of this species from the genus 
Aposphaeria Berk., and the placing of it in the genus Plenodomus Preuss, 
1 Published with the permission of the Director of the Michigan Agricultural Experiment Station. 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
bt 
(713) 
Vol. V, No. 16 
Jan. 17, 1916 
Mich .—2 
