[Vor. 4 
306 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
or gyrose, while the departure from the even hymenial sur- 
face in the genera of the Thelephoraceae just named is at the 
most only undulate-tubercular or granular. Greater difficulty 
may be experienced in deciding from poor or scanty material 
whether a given collection belongs in Merulius or in Poria. 
The development of the hymenium is, however, fundamen- 
tally different in these two genera. In Merulius, the hymenium 
is at first plane, and in this young stage sections show basidia 
and spores; by further growth this plane surface is thrown 
into folds and becomes porose, but it remains continuous over 
this irregular surface and will show in sections basidia on 
the edges of the folds as well as lining the pores. In Poria 
the formation of pores precedes the formation of the 
hymenium, hence sections of a young Poria having distinct 
pores may have no basidia as yet; at length a hymenium de- 
velops for each pore, as in the genus Porothelium, but these 
hymenia are not continuous over the edges of the dissepi- 
ments from pore to pore, so far as I have observed; hence 
while a рогове Merulius and а Poria may resemble each other, 
sections of the Merulius should show a continuous hymenium, 
while those of the Poria might have the hymenium not yet 
differentiated if the Poria is very young, or lacking the 
hymenium on the edges of the dissepiments if mature. 
The species of Merulius are of great economie importance 
on account of the dry rot of timber, caused by the species 
which grow on wood. There is an extended literature on the 
dry rot caused in Europe by Merulius lacrymans, a species 
which is rather rare in North America; but very little has 
been published in the United States concerning decay caused 
by our numerous other species. 
I am indebted for specimens to my correspondents whose 
names are mentioned in the following pages, and who have 
made possible this record of our species of Merulius and of 
their distribution. I am under further obligation to Dr. W. A. 
Murrill for the opportunity to study the unmounted speci- 
mens of Merulius of the New York Botanical Garden Her- 
barium, to Mr. C. G. Lloyd for permission to study his refer- 
enee series of species of Merulius, to Dr. H. D. House for 
