THE EXTENT OF THE HYMENIUM 29 



for which the gills, tubes, or spines are responsible. Let the 



Fig. 5. — Under surface of fruit-body of Polyporus squavio-ius nearly full-grown, 

 showing the pores of the hymenial tubes and the reticulations on the stipe. The 

 fruit-body was photographed immediately after it was cut : the involution of the 

 edge of the pileus is quite natural. Photographed by R. H. Pickard. ^ natural 

 size. 



specific increase of hymenial surface, due to the presence of gills, 



