EUASCOMYCETES 189 



hyphae grow side by side, and coil once or twice. The terminal cells 

 elongate and fuse near their tips. Ascogenous hyphae grow from the 

 basal cell of one of these hyphae, suggesting that there is a differentiation 

 into trichogyne and ascognonium, although the nuclear history could 

 not be followed in the material available. The ascogenous hyphae 

 produce asci in most of their cells, as in the Onygenaceae and Trichoco- 

 maceae (C. W. Dodge, 1928). 



In M . castanea, the hard central core has comparatively few trabec- 

 ule connecting it to the peridium which at maturity consists of a 

 single layer, suggesting the peridium of Elaphomyces muricatus in its 

 mottled appearance. In M. sabulosa, the peridium is cut off from the 

 gleba by a well marked zone of fission and quickly gelifies so that at 

 maturity it consists largely of a shell of sand held together by a gel. In 

 M. arenaria, the rind is differentiated into a peridium and cortex having 

 the texture of strawboard as seen in section. 



Elaphomyces forms mycorrhizas with the roots of conifers, (Fig. 119, 

 A-B) especially E. muricatus, E. variegatus and E. cervinus. The latter 

 has been used since the Middle Ages as an aphrodisiac in folk medicine. 

 All three species are often infected with Cordyceps ophioglossoides and C. 

 capitata of the Hypocreales. 



Summary. — The Plectascales hold an important position in the 

 Ascomycetes as below they have their morphological relations with 

 the Endomycetales and Zygomycetes, and have the beginnings of a 

 varied upward development. Their imperfect forms, conidia, are 

 basically the same as in these groups, but they have developed in three 

 directions. One is represented by the Aspergillaceae ; morphologically 

 it inclines toward the Syncephalastrum-Syncephalis group and in this 

 sense forms a branch of the Choanephora-Piptocephalis series. While 

 in Mucor, Sporodinia, etc., spore formation is still normally endogenous, 

 in Choanephora, with liberal food, it is retarded and becomes exogenous, 

 and in Syncephalastrum and Syncephalis it is fixed in an exclusively 

 exogenous type. The Aspergillus group has proceeded a step beyond 

 the Syncephalis type, however, and on its sporangia forms purely 

 exogenous conidia. Just as in the further development of the Synce- 

 phalis type, the sporangia which have become functionless collapse into 

 gibbous basal cells (as in Piptocephalis) ; in the Aspergillus group the 

 sporangia degenerate and through a series of intermediate forms the 

 Penicillium type is reached, where long spore chains on flask-shaped 

 phialides are cut off at the top of undifferentiated conidiophores. 



The second direction is represented by Thielavia. Its origin is still 

 unknown; its morphological significance lies in endogenous conidial 

 formation by the splitting of the conidial membrane. The third direc- 

 tion is represented by Ctenomyces. Here for the first time the condio- 

 phores intertwine into special pycnia with lysigenous cavities. 



