30 



in older ones. It i.s composed of looseh' interwoven hypha?, Avhich 

 form a continuation of the main hvphal strands which compose the 

 body of the pileus. The hyphae of the latter start from a central 

 point on the bark and radiate out in several directions (PI. IX, fig. 7), 

 forming a mesh which at first is very loose. The h3^ph^ are almost 

 colorless and have a decided lumen. As they grow older their walls 

 become brown and very thick, so that the lumen is reduced to a ver}^ 

 small one. The peripheral growth of the h^^pha? takes place in such 

 a wa}" as to form well-defined layers. For several years these hwers 

 are added one outside of the other. The lowermost portion of each 

 layer is usualh^ less dense than the outer portion, and after the h^^ph^ 

 turn brown large masses of cr^^stals of calcium oxalate are deposited 

 in the meshes of the outer portion. The alternation of laj^ers of less 

 densit}^ with those of greater density makes a differentiation of layers 

 possible. The layers vary considerably in width (PL IX, figs. 5-7), 

 and it is suggested that this is probabh^ due to varying conditions; 

 probably the amount of food supplied and the amount of available 

 moisture exert a marked influence. The pileus grows in width and 

 length by the direct elongation of the hyphas of the last layer. After 

 several years' growth the hyphae on the under side of the developing 

 shelf grow down in a vertical direction and give rise to the pores. 



The pores are ver}^ long and are continuous from year to year. 

 After a time they become plugged at the bottom b}" hypha? Avhich 

 grow into them from all sides. Different sporophores differ in this 

 respect. With some the pores are open through eight or ten of the 

 recent laj^ers; in others the growth -of hyphee is so vigorous that the 

 pores are closed almost as rapidl}" as they are formed. The hymenium 

 arises on the surfaces of the pores from h3^ph^ of the trama which 

 turn at right angles to the general direction of the tramal hyphae. 

 The latter have very thick walls (PL IX, fig. 12) and extend longitudi- 

 nally, forming a very loose network. The tips of those hyphae which 

 form the h^^menial layer are thin walled. The hymenial layer itself 

 is composed of hyphae of almost equal width. The layer is a very 

 narrow one. Cystidia are practically absent. The basidia barely 

 rise above the general surface and do not differ materially in form 

 from the paraphyses. The four spores are colorless. Amid the 

 tramal and hymenial hyphae accumulations of calcium oxalate crystals, 

 colored red-brown, occur in great numbers, likewise large quantities 

 of an oil readily soluble in ether and becoming solid at about 59^ F. 

 (15^ C). The growth of the h^^menial layer is very irregular. At 

 one and the same time pores may be forming on one side, while at the 

 opposite side the old pores are completely plugged. The hymenium 

 renews itself at frequent intervals. The vitality of its hj^pha? is very 

 great, for it is not at all rare that insects eat away a considerable por- 

 tion of the lower side of the pileus. These parts die and turn brown. 



