[Vor. 5 
2 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
darker; cavities irregular, subequal, at first hollow, then 
more or less filled with spores; septa homogeneous or scis- 
sile, composed of branched interwoven hyphae, often gelatin- 
izing at maturity; basidia varying from ovoid to cylindrical, 
2-8-spored; spores ellipsoidal, unicellular, 1-2-guttulate, 
sometimes appearing 2-celled at maturity, due to the peculiar 
position the nucleus assumes. 
In 1817 Fries and Nordholm described Rhizopogon luteolus, 
and Fries (1823) added three species, one of which proved to 
be an ascomycete, and the other two, synonyms of R. luteolus. 
Vittadini, Corda, and others treated the genus as ascomy- 
cetous, considering Rhizopogon albus Fries (1823) as the 
type. Corda (1831) described Splanchnomyces, with S. rose- 
olus (see p. 16) as the type, and later added many other 
species which are to be looked for in various modern genera 
of the Hymenogastraceae. Vittadini, after having Hyste- 
romyces in manuscript for several years, published it, with 
H. vulgaris (Rhizopogon rubescens var. Vittadinii Tulasne) 
as the type, in the same year (1844) in which Tulasne 
emended the genus Rhizopogon Fries & Nordholm. 
Not until a later paper will we attempt a discussion of the 
relations of Rhizopogon to the other genera of the Hymeno- 
gastraceae, but the taxonomic study of the genus has un- 
earthed a series of forms which anticipate a very interesting 
morphological development within the genus, should sufficient 
histological study be possible. We refer here particularly to 
the simplex and duplex character of the peridium. The outer 
layer of the duplex forms is sometimes very thin (R. macu- 
latus) or often is thick and cracked (R. pannosus and R. 
Briardi). Is the thin outer layer of some of the species of 
Rhizopogon comparable to the universal veil or ‘‘blemato- 
gen’’ found in the button stage of some of the evolvate agarics 
and reported by Conard! in Secotium agaricoides? Or, is the 
thick, cracked, outer layer of such forms as R. pannosus and 
R. Briardi comparable to the volva of certain Agaricaceae 
and Phallaceae? These questions can be answered only after 
nard, Н. S. The structure and development of Secotium agaricoides. 
Mycologia 7: 94-104. pl. 157. 1915 
