106 STUDIES OF AMERICAN FUNGI. 



depending on the depth of the insertion of the stem in a hollow por- 

 tion of the trunk. The plant is white or whitish, and the substance 

 is quite firm, drying quite hard. 



The pileus is convex to expanded, more or less depressed in the 

 center, the margin involute, and the surface at first floccose, becom- 

 ing in age floccose scaly, since the surface breaks up into triangular 

 scales more prominent in and near the center, smaller and inconspic- 

 uous toward the margin. The prevailing color is white, but in age 

 the scales become cream color or buff (in European plants said to 

 become fuscous). The pileus is either definitely lateral (Fig. io6) 

 or eccentric when the stem is attached near the center as in Fig. 107. 

 The gills are white, becoming tinged with yellow in age, decurrent 

 (running down on the stem) in stride for short distances, 4-5 mm. 

 broad, not crowded. The stem is nearly central (Fig. 107), or 

 definitely lateral (Fig. 106), the length varying according to condi- 

 tions as stated above. It is firm, tough, fibrous. The veil is promi- 

 nent in young and medium plants, floccose, tearing irregularly as the 

 pileus expands. 



Figure 107 is from plants (No. 2478J C. U. herbarium) growing 

 from knothole in living hickory tree, and Fig. 106 from plants (No. 

 2478/') growing on a dead stump, near Ithaca. 



According to the descriptions of P. diyimis as given by Persoon, 

 and as followed by Fries and most later writers, the pileus is defi- 

 nitely lateral, and more or less dimidiate, while in P. corticatus Fr., 

 the pileus is entire and the stem rather long and eccentric. Steven- 

 son suggests (p. 166) that corticatus is perhaps too closely allied to 

 dryimis. The plants in our Fig. 108 agree in all respects with P. cor- 

 ticatus, except that possibly the lamellae do not anastomose on the 

 stem as they are said to in corticatus. According to the usual descrip- 

 tions corticatus is given as the larger species, while Fig. 106 of our 

 plant, possessing the typical characters of dryinus, is the larger. The 

 form of the pileus, the length and position of the stem, depends, as we 

 know, to a large extent on the position of the plant on the tree. 

 When growing from the upper side, so that there is room above for 

 the expansion of the cap, the pileus is apt to be more regular, just as 

 is the case in Pleurotus ulmarius, and the stem more nearly central. 

 When the plant grows from a hollow place in the trunk as those 

 shown in Fig. 107 did, then there is an opportunity for them to grow 

 more or less erect, at least iintil they emerge from the hollow, and 

 then the pileus is more nearly equal in its expansion and the stem is 

 longer. Berkeley describes specimens of P. dryinus with long stems 



