THE ANATOMY AND OTHER FEATURES OF THE BLACK KNOT 1 25 
broken up segments of the cambium opposite the broad rays, and not 
from the breaking up of the entire cambium. 
12. Scalariform tracheids are formed by many of the misplaced 
cambium cells in the cortical portion of the knot. Only pitted 
tracheids occur in normal adult wood. 
13. The proportional increase in the thickness of both wood and 
bark is about the same in the development of the knot. 
14. The outer portion of the bark is not altered materially and is 
sloughed off just before the conidia appear. 
Methods 
In preparing sections for study and photomicrographing it was 
found, after considerable experimenting, that the best results could 
be obtained by cutting the knots without imbedding. Sections lO/j. 
in thickness could be easily obtained in this way which were thin 
enough for what was required. Where softer portions alone were to 
be studied the usual paraffin method was employed. Iron-alum 
haematoxylin and safranin were used by the usual method employed 
in staining wood sections, except that after removing the excess of 
safranin in 95 per cent alcohol the sections were transferred for a 
short time to acid alcohol and then to weak ammonia water. Without 
this, good differentiation was not obtained. 
The writer wishes to express his thanks to Professors Farlow and 
Thaxter for the many courtesies shown him while he was working in 
their laboratories at Harvard University. He wishes also to thank 
most heartily Professor L. R. Jones, of the department of plant path- 
ology, and Professor C. E. Allen, of the department of botany, Uni- 
versity of Wisconsin, for much advice and assistance. 
The negatives for figs. 2 and 10 were made by Mr. M. E. Diemer 
of the Forest Products Laboratory. 
Department of Botany, 
University of Wisconsin, 
Madison. 
