156 MR. R. H. BIFFEN ON THE 
distinguished from the cells of the hymenial layer at an early 
period, for instance in sporophores 3 mm. high. 
The growth of the sporophore, until it reaches its full 
size, is now very rapid, but no new points of interest were 
brought out in investigating it. It should be remembered that 
the measurements given above are from cultures which are 
smaller than those grown under more natural conditions. 
In order to investigate the action of the fungus on the wood, a 
series of infected blocks were prepared at intervals of a week or 
fortnight. The first few were fixed with Flemming's solution, 
well washed in water, and taken through 50, 70, and 90 per 
cent. to absolute alcohol. This method was found to dissolve 
the lignin slightly from the elements at the edges of the blocks, 
and was therefore abandoned. Instead, the blocks were boiled 
for a short time, to fix the hyphe in situ, and then taken through 
the same series of dilutions of alcohols as before. 
On rubbing off the outer mycelium the wood was found to be 
marked with dark brown patches and lines, or, if the culture was 
an old one, it was a uniform brown all over, but the affected 
parts were still hard and showed no signs of disintegration. To 
trace the course of the mycelium, dilute Delafield’s hzmatoxylin 
and picric-aniline-blue were used as stains. Radial sections of a 
block infected a week previously show that the oidia on the 
surface of the wood have germinated, and that the hyphæ they give 
rise to have penetrated several layers of tracheids in depth into 
the wood. Possibly on account of chemotaxis they enter chiefly 
through the pitted walls of the medullary rays. If a transverse 
surface is infected they penetrate for the most part by the wide 
vessels. All stages in the germination of the oidia and the pene- 
tration of their hyphe occur in cultures of this age (PI. 3. fig. 11). 
As soon as the hyphæ have formed a small mycelium in the 
vessels and tracheids, it is again broken up into oidia (PI. 3. fig. 12), 
which quickly germinate, for very few are to be found in eultures a 
week older, and thus the wood is permeated by a large mycelium 
in a short time. In fact in cultures three to four weeks old it is 
difficult to find any of the wood elementa free from hyphe which 
have penetrated through the pits of the walls, the medullary rays 
again serving as the easiest path into the wood-elements (Pl. 3, 
fig. 13). 
Strands of shortly septate hyphe then begin to form (PI. 4. fig, 
14), which ultimately push their way through the wood to the 
