38 BULLETIN 175, U. S. DEPARTMENT OF AGRICULTURE. 



Hymenophore sessile, corky, tubes sinuous and labyrinthiform Daedalea. 



Hymenophore reflexed, resupinate or amorphous, subgelatinous, 

 hymeniurn plicate or rugose porous Merulius. 



BOLETUS. 



In general appearance, namely, the pileate and stipitate character 

 of the plants, the species of the genus Boletus resemble members of 

 the Agaricacese. The important difference is the fact that the spores, 

 instead of being developed on gills, are borne in numerous small 

 tubes, which are closely crowded but easily separable from one 

 another and from the hymenophore. 



Most of the plants of this genus are terrestrial, but occasionally 

 they are to be found growing upon wood. Some species are edible 

 and considered exceedingly good, while others are extremely dan- 

 gerous. The phenomenon of changing color on exposure to air 

 exhibited by certain species is not a character peculiar to either 

 poisonous or edible varieties. 



Key to species of Boletus. 



Surface of hymenium yellow, orange, or greenish. 

 Ring present: 



Cap yellow B. luteus. 



Cap brown when moist, yellowish when dry — 



Stem long, granulated B. granulatus. 



Stem short, not or rarely granulated B. brevipes. 



Ring absent: 



Flesh not changing color — 



Mouths of tubes white becoming tinged with flesh color. . .B. felleus. 



Mouths of tubes white becoming yellow and greenish B. edulis. 



Flesh or tubes or both changing color — 



Tubes adnate or sinuate, depressed, tinged with green B. badius. 



Tubes free, yellow, mouths bright red, orange colored in 



age B. satanus. 



Tubes subadnate, large, angular, flesh red immediately 



beneath the cuticle, changing to blue where wounded. B. chrysenteron. 

 Tubes adnate, small, subrotund, bright yellow, changing 



to blue where wounded B. bicolor. 



Boletus bicolor. (Edible.) 



Cap convex, glabrous, pruinose, dark red, paler in age and sometimes spotted with 

 yellow, firm; flesh yellow, sometimes changing to blue where wounded; tubes 

 nearly plane, adnate, bright yellow, changing to blue where wounded, mouths small 

 angular or subrotund; stem subequal, solid, red, generally yellow at the top. 



Cap 2 to 4 inches broad; stem 1 to 3 inches long. 



A very attractive little species, occurring quite commonly in Virginia and Maryland 

 in the woods and on lawns in shady places. It is considered one of the best edible 

 species. 



Boletus chrysenteron. 



Cap convex or plane, brown or brick red, more or less cracked, subtomentose; 

 flesh yellow, red immediately beneath the cuticle, slightly changing to blue where 

 wounded; tubes subadnate, yellow then greenish, large, angular; stem fibrous, 

 equal, red or yellowish. 



