Overholts: Diagnoses of American Porias 



7 



and measure 6-7 x 2 fju, consequently longer and more slender in 

 proportion than in P. ferrugino.su. In most cases there is an addi- 

 tional difference in the setae, which here project only 15-20 fi (PI. 

 I, figs. 3-4), or at most not more than 27 /x, beyond the basidia, 

 while in P. viticola they are usually much longer, sometimes pro- 

 jecting as much as 60 /x beyond the basidia. However, a few col- 

 lections of P. viticola have been noted in which this distinction 

 does not hold, but in which the setae are quite like those of P. fer- 

 ruginosa. In such cases the importance of the spores as a distin- 

 guishing character is much enhanced. Of course, some collections 



Fig. 4. a, Hyphae of P. ferruginosa ; b, Spores. 



do not contain spores, and other characters must be used in dis- 

 tinguishing between this species and its allies. However, the dif- 

 ference between the setae in ordinary cases is striking, especially 

 if they be compared side by side under the microscope. Occasion- 

 ally the hymenium of P. viticola is somewhat daedaloid — a condi- 

 tion never seen in P. ferruginosa. 



Porta marginella Peck is a similar species on coniferous wood, 

 but its spore characters are those of P. viticola. 



The decay caused by this fungus is of the general delignifying 

 type, producing a uniform whitening and softening of the sap- 

 wood. No striking characteristics are shown by it. The fungus is 

 apparently not an organism inducing rapid decay, and as it is 

 almost entirely confined to the smaller branches is not of great 

 economic importance in producing timber loss. 



Poria nigrescens Bres., Atti Accad. Rovereto III 3 : 83. 1897 



Original Description: Late effusa — subiculo membranaceo, stra- 

 mineo, facile separabili, 1— 1.5 mm. crasso ; tubulis concoloribus, 

 usque ad 2 mm. longis ; poris parvis, subrotundis, in vegeto albis, 

 dein pallide carneo-violaceis, demum nigrescentibus ; hyphis sub- 

 hymenialibus tenuiter tunicatis, 4-6 /x latis ; sporis non visis. 



Perennans, stratosus, tubulis singolorum annorum strato inter- 

 medio floccoso distinctis. 



