HYMEXOGASTRACEAE 27 



are other cells of the hymenium, and the supposed sterigmata are probably the col- 

 lapsed basidia lying among them. In all species we have seen the basidia are very 

 delicate and soon collapse. 



A very peculiar species is R. parasiticus, which grows as a parasite on the rootlets 

 of pine. It is the only one of our subterranean Basidiomycetes which is certainly known 

 to be a parasite. Rliizopogon graveolens has been reported by Zeller and Dodge from 

 Alabama (Earle, coll.). Through the kindness of Dr. C. L. Shear we have seen a good 

 plant of this collection and find that it agrees well with our R. rubescens, No. 1932. 



Literature 



Lloyd. The Genus Rliizopogon. Myc. Notes, p. 1170, figs. 2312-2322. 1923. 

 Zeller and Dodge. Ann. Mo. Bot. Garden 5: 1. 1918. 



Key to the Species 



Parasitic in clusters on the roots of pine; plants small R. parasiticus (p. 27) 



Not noticeably parasitic; plants larger 



Spores without a cup and not appearing truncate 

 Peridium composed of a single layer 



Cavities only partially filled with spores at maturity 



Fibrils few; peridium in section reddish brown to black when treated with 7% KOH 

 Peridium when cut turning pink or rosy throughout; spores 2-2.7 x 5.5-7.4// 



R. rubescens (p. 28) 

 Peridium when cut turning rosy in inner part only, outer part remaining citron 



yellow; spores 3-3.7 x 6.4-8.5/* R. roseolus (p. 32) 



Fibrils many; peridium turning distinctly purplish in section when treated with 7% 



KOH; plants deep sordid brown to black when dry R. nigrescens (p. 30) 



Cavities filled with spores at maturity; fibrils many 



Surface woolly; septa 60-90^ thick; odor unpleasant R. luteolus (p. 33) 



Surface not woolly; septa 74-111m thick; odor pleasant R. piceus (p. 34) 



Peridium double; many of the cavities filled with spores at maturity R. maculalus (p. 35) 



Spores with a vague cup which is often extended into a collapsed filament (a part of the basidium), 



but spores scarcely truncate, 3.7^1.6 x 8-ll/i R. luteolus (p. 33) 



Spores with an open cup on the proximal end and thus appearing truncate; glebal chambers very 

 small and barely visible without a lens 



Spores 3-3.7 x 7.4-8.5/» R- atlanticus (p. 35) 



Spores 3-4.4 x 6.8-7.2/i R- truncatus (p. 36) 



Rhizopogon parasiticus Coker and Totten 



Plates 19 and 20 



Fruit body up to 1.5 cm. broad and high, though usually much smaller, the great 

 majority about 2-5 mm., sometimes almost evenly globose but more often lobed and 

 convoluted; attached at any point to one or several branching, flocculent, rhizomorphous 

 threads which run in the humus and connect the fruit bodies on different roots; rarely 

 some of these branching threads may run along and cohere with the surface of the 

 fruit body; color of both mycelium and the fruit body varying from a light ochraceous 

 salmon to a warm buff at all ages until decay sets in. Peridium of mature plants du- 

 plex, 50-1 30/i thick, the outer layer a spongy mass of loosely woven threads that col- 

 lapse when the plant is cut or bruised or when decay sets in; the inner layer more closely 

 woven, lighter in color and intimately connected with the internal hyphae; threads of 

 the peridium soft and delicate, 2.6-lOA/i thick, in young plants more closely woven. 



Gleba when fully formed containing many cavities that are minute, irregular, 



