1914] 
BURT—THELEPHORACEJE OF NORTH AMERICA. I 195 
The microscopical technique has been simplified as much as 
possible. Usually dried herbarium material had to be used for 
study and proved very satisfactory except in the case of speci- 
mens which had been subjected to poisoning processes for pres- 
ervation in herbaria. А small bit of the fructification having 
a promising hymenial surface 2 or 3mm. square—but smaller if 
the specimen is a valuable type—is first moistened with alcohol, 
then wet with water and cut out from the rest of the specimen 
and from the substratum. This bit is then placed in a holder 
of elder pith and oriented so that the sections may be cut per- 
pendicular to the surface of the hymenium and also contain as 
long hyphe as possible. The sections are cut as thin as possible, 
free hand, with a very keen section razor flooded with alcohol. 
The thinnest sections are placed on a slide in a drop of water 
and then a drop of seven per cent aqueous solution of potassium 
hydrate is added. 
Close observation of the sections should be made when the 
potassium hydrate solution comes in contact with them. For 
most species, the sections are merely cleared and the hyphe 
swelled to the normal size of vegetative hyphe. Ina few species, 
the alkaline solution may dissolve out the color of the section 
on coming in contact with it, or it may change this color to a 
violet, which finally disappears, or it may cause disorganization 
changes in certain structures leading to their disappearance or 
destruction. Such changes should be observed and noted, for 
they are of help in the determination of the species. In the 
cases in which potassium hydrate solution exerts a destructive 
action, lactic acid should be employed with other sections in 
the manner described for potassium hydrate. Lactic acid 
clears and swells sections well, but so much more slowly than 
potassium hydrate that I have used it only where the latter is 
not satisfactory. After the sections have been cleared, the 
potassium hydrate should be drained off, the sections lightly 
stained on the slide with alcoholic solution of eosin (but not 
overstained), mounted in water, and studied at once. 
For a thorough study of the species of the family at least one 
permanent preparation of each species should be retained for 
future comparisons. Permanent preparations may be made 
from the temporary water mounts by adding dilute glycerin— 
