84 THE P0L7P0BACEAE OF WISCONSIN. 



Largest specimen foimd was on a poplar at Horicon and measured 

 nearly y2 meter in width, about 24 cm. in length and 15 cm. in thick- 

 ness near its base. It shows about 10 or 12 strata,, the older ones some- 

 what indistinct. The pilei are usually sessile, sometimes substipitate — 

 especially those growing from the roots of stumps and trees — often 

 imbricated. The young growth is pure white, soft, moist and turns 

 brown when injured. It then hardens into a whitish-gray crust which 

 soon becomes brown-pulverulent due to the numerous spores which are 

 scattered on the pileus either by currents of air or by overhanging 

 pilei. Sticks and stones lying beneath are usually likewise covered. 

 The spores are ovoid and about 6 to 7 microns in diameter. 



The species varies in form from very thin explanate to thick ungu- 

 late; it is easily recognized by the whitish horny crust, the white- 

 pruinose hymenium which turns brown when bruised, and the dark 

 ferruginous context made up of the two layers of homy fibers — one go- 

 ing upwards to form the crust and the other turning down to form the 

 tubes. In most stratified specimens examined there are traces of the 

 hymenophore between the strata (PI. IX., fig. 31). Old specimens are 

 often black and rimose. 



Eelated to F. reniformis, F. fomentarms and F. vegetus. Distin- 

 guished from the first by its thicker crust and harder consistency ; from 

 the second by its smaller and shorter pores and by being flat instead of 

 ungulate; from the last it is said to be distinct because it has thicker 

 flesh and is not supposed to have the "floceose layer" separating the 

 strata. 



With Atkinson I cannot follow Lloyd (12 p. 60) in the conclusion 

 that the American forms referred to this species are in i%ality to be 

 identified with F, leucophaeus Mont., and that F. reniformis Morg., is 

 F. applanatus (Pers.). Lloyd's view is that in general the two species 

 are very much alike, but that F. applanatus has softer tissue and 

 echinulate spores, while our common form (F. leucopJiaeus) has smooth 

 spores. 



The forms of F. applanatus as I have identified them agree very well 

 with the specimen of F. applanatus No. 302, Sydow's Mycotheca ger- 

 manica, from the Hartz mountains. The spores of the German speci- 

 men also are smooth like those of ours and of the same shape. The 

 tissue is no softer in Sydow's specimen than in ours, except in the case 

 of very old forms which may become unusually hard in some cases. 

 I also find that our common forms often interpose a new stratum of 

 hymenophore between the first and second year's growth, as Morgan says 

 is the case in F reniformis; still I am inclined to think that Morgan's 

 form is distinct. 



