1915] 



OVERHOLTS STUDIES IN THE POLYPORACEAE 



699 



chioneus and accepting Fries ' idea of P. lacteus, it becomes an 

 easy matter to differentiate between P. chioneus and P. albel- 

 lus. As stated above, and as will be seen in the accompanying 

 illustration (fig. 4), the hyphae in the context of P. albellus 

 are unbranched or at most very infrequently branched, while 

 those of P. chioneus (fig. 3) are branched to a very great de- 

 gree, and they vary considerably in size, some being narrow 

 -6 n) and others twice as thick. This is not the only dis- 

 tinguishing character, nor 



the one that was first hit 

 upon by the writer, al- 



though it is probably the 

 most reliable. The rela- 

 tive thinness of the pileus 

 in proportion to its length 



is a distinguishing char- 

 acter of P. chioneus. In 

 other words, the pileus is 

 usually thin and spreading 

 in P. chioneus, while in P. 



albellus it is thicker, con- 

 vex or ungulate, and triangular in section. This is only 



a general statement of a character that varies considerably. 



An additional character is found in an examination of a 



cross-section of the hymenium, though the sections must 

 be cut very thin to see it at its best. In sections of 



P. albellus the hyphae in the trama of the pores appear to 

 run in all directions and give a peculiar, ever-changing ap- 

 pearance as they are viewed at changing foci. They are also 

 all of one size. In P. chioneus the hyphae in the trama of the 

 pores all run in one direction and practically all are cut trans- 

 versely in a cross-section of the hymenium. The trama is seen 

 to be made up of a background of a pseudocellular structure, 

 with minute openings that indicate the cavities of the closely 

 compacted hyphae. Interspersed over this background one 

 sees cross-sections of hyphae two to three times larger, and 

 standing out much more plainly than the sections of the com- 

 pact hyphae in the background. It was at first thought these 



Fig. 4. 



Hypliae of P. albellus. 



