56 College of Forestry 
many xerophytic plants. It is generally accepted that the 
hairs on the leaves of xerophytic plants serve to reduce 
materially the transpiration. It is therefore reasonable to 
suppose that the hairy covering protects the sporophores of 
fungi from rapid dessication. In support of this it may 
be mentioned that a pileus stripped of its hairy surface dries 
up far more rapidly than it otherwise would do. 
The surface modifications are almost the only differentia- 
tions that the tissues of the sporophore undergo. Conse- 
quently they should be considered as important characters 
in any arrangement of the plants on a structural basis. 
The Hymenophore.— From a taxonomic point of view the 
hymenophore is an important part of the fruit body since 
its poroid character separates the family Polyporacew from 
all related families excepting the Boletacew. ‘The boletes, 
however, differ from the polypores chiefly in that they are 
mostly centrally stipitate plants of fleshy consistency and a 
terrestrial habit, in which the tubes can be separated readily 
from the pileus in most species. All plants belonging to the 
Polyporaceee, at few exceptions, have the pordid: configura: 
at least in early youth. In 
Polyporus pargamenus, oe, which is poroid at first, 
the dissepiments generally become torn into teeth or lacerate 
plates soon after the formation of the pores, so that older 
specimens might easily be mistaken for one of the Hydnacee. 
Development of the Pores.—In Polyporus pargamenus 
the pores are evolved successively from the center or point 
of attachment outward and are open from the beginning as 
is the case with the majority of polypores. Such pores are 
said to be formed exogenously. In the case under considera- 
tion they arise directly from a layer of hyphze differentiated 
from the trama. A section through the growing margin 
shows the early stages of pore formation. On the lower 
side of this portion of the pileus the hyphz are more closely 
interwoven and smaller and instead of the hyphz extending 
parallel with the surface they are arranged obliquely. In 
section a few hyphz can be seen that grow more rapidly than 
