4 
difficulty of naming would be a serious disadvantage, if it were 
not that the same remedies can be applied in nearly every case- 
There is great room for experiment in the artificial culture of these 
economically important fungi by those who have time and facilities 
placed at their disposal in the phytopathological institutions now 
so numerous, and it is strange that (with two or three exceptions) 
so little work has been done in this direction by professional 
mycologists. Still, when the host is known, there are certain 
characteristics of most of the species which will lead to a probable 
conclusion, and this may be converted into certainty by dis- 
covering the Valsa-stage. 
In conclusion, perhaps it will be permissible to recount two 
experiences among my own which will illustrate what sort of 
evidence can be obtained without test-tubes or pure cultures. 
When one says that the Cytospora and the Valsa occur together, 
that in itself goes for little, or is at best only suggestive, as eve 
one would admit; it is the way in which they occur together that 
is convincing. 
First example :—In the summer and autumn of the year 
- 1918, the fungus which is described below as C. Oxyacanthae was 
extremely common round Birmingham on hawthorn cuttings 
left lying in ditches and on the hawthorn stakes driven into the 
ground by the hedgers to support the pleached hedges. Mr. 
D. A. Boyd reported to me exactly the same state of things 
in the south-west of Scotland. By continuing to look in suitable 
places, at last, in March and April, 1919, I came across a number 
of branches which yielded ascospores dispersed among the still 
remaining Cytospora pustules, and when once seen they could 
be found elsewhere in similar positions and in great quantity. 
It was a disappointment that the ascophorous stage turned out 
to be hardly distinguishable from normal Valsa ambiens, and 
could at most be considered only one of the forms into which 
that collective species will have to be subdivided. But of the 
genetic connection between the two stages no one who had 
observed the facts could have had the slightest doubt. One 
could constantly find the Cytospora pustule surrounded by a 
ring of perithecia whose mouths bordered the disc. 
Second example :—In a large park, which need not be further 
particularised, numbers of poplar trees of various species were 
thickly covered, especially on the smaller branches, with the 
orange-yellow tendrils of Cytospora chrysosperma. Many of the 
trees (some young) were obviously dying, and one of them (about 
twenty feet high), which was most severely attacked, was already 
nearly dead. When the top of this was lopped off, it was found 
that the main stem, a little over one inch in diameter, was com- 
pletely occupied for about four feet by a crowd of Valsa pustules. 
‘These on examination were seen to be Valsa sordida, the branches 
of the lopped portion and the upper part of it being as thickly 
covered by the Cytospora. If the top part of the tree had not 
been lopped off, the Valsa-stage might easily have escaped 
observation. Here, again, there could be no faintest doubt of 
