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 Polyportts sffuanioxus 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 bv R. H. Pickard. ^ natural 

 size. 



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



