SOME OBSERVATIONS ON THE ANATOMY AND OTHER 
FEATURES OF THE "BLACK KNOT" 
Alban Stewart 
WITH PLATES IX AND X 
Some three years ago, while I was connected with the department 
of botany in the New Hampshire Agricultural College of Durham, New 
Hampshire, I became interested in the study of the "black knot" 
fungus, Plowrightia morhosa (Schw.) Sacc, which causes the black 
enlargements on the branches of plum and cherry trees, and from 
which character the fungus receives its common name. A consider- 
able amount of material was collected from Prunus virginiana L. in 
that vicinity at intervals of two or three days, from the early part of 
May until July, and properly preserved for future study. I also made 
some cross inoculations on the cultivated plum, but as I was called 
elsewhere soon after this, I did not pursue this part of the work 
further. I began the study of my material in Professor Thaxter's 
laboratory at Harvard University about six months after I left Dur- 
ham, but after sectioning it was found that the material was all too 
old when it was collected to show early stages of development of the 
knot, so I abandoned the work for the time being. 
Upon coming to the University of Wisconsin in the autumn of 
191 1, I found that my colleague. Professor E. M. Gilbert, had already 
begun the study of this fungus, and as neither of us had progressed 
far at this time, we agreed to divide the work. Professor Gilbert to 
study the morphology of the fungus while I was to confine my work 
to the anatomy of the knot itself. The results I have obtained are 
given in the following pages. 
Papers dealing with this fungus in a general way are very numerous, 
probably owing to its wide distribution in this country. Nearly 
every Agricultural Experiment Station, in the states where this 
fungus occurs, has dealt with it more or less with reference to methods 
of eradication and control. Papers, however, on the morphology of 
the fungus and of the knot itself are very few, owing possibly to the 
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