TUBER ALES 361 



endogenously. In the youngest known stage, measuring about 34 mm. 

 (Fig. 242, 1), as in many lichens, e.g., Physcia pulverulenta, Anaptychia 

 ciliaris and Usnea barbata, the hymenial palisade is formed angiocar- 

 pously at the tip of the fructification under the outer rind Ra. In course 

 of further development, the margins bend over strongly so that the fertile 

 layer becomes patelliform (Fig. 242, 2 and 3). Later, by a strong lateral 

 growth, it gradually forms a comparatively smooth hollow sphere, in 

 which the hymenium (Fig. 242, 4) is not free but covered by the rind Ri 

 which consists of swollen and septate paraphyseal tips and corresponds 

 apparently to the epithecium of the Pezizales. 



From Genea Thwaitesii, the development may be followed in two 

 directions. In Genea the same process which we have met in the develop- 

 ment of ascocarps of Tuber, is repeated. In the subgenus Heterogenea, 

 (G. (Heterogenea) Gardneri and G. (Heterogenea) Harknessii) numerous 

 ingrowing projections of the cavity tend to separate the fertile areas, 

 while the spores become less ellipsoid. In the subgenus Myrmecocystis, 



Fig. 244. — Genabea fragilis. (X 5; after Tulasne.) 



however, the spores have become spherical and verrucose. If we only 

 had the end members of the series we would probably regard them as 

 separate genera, but the transition forms seem to indicate that they are 

 better kept together. 



Thus the hymenium is no longer laid down in a continuous layer, but 

 separated into several parts by sterile ground tissue, as may be seen in 

 Fig. 243, 1, in (?. (Myrmecocystis) Vallisumbrosae, which consists of 

 irregular, spherical, hollow fructifications, occasionally slightly plicate, 

 about 1 cm. in diameter with one or two round fissures. Thus the sub- 

 genus Myrmecocystis differs from Eugenea, as Piersonia from Pachy- 

 phloeus, by the localization of the hymenium on limited areas. As in the 

 Sphaerosoma-Hydnotrya series, here the wall of the fructification curved 

 into the interior of its cavity with folds and projections and thereby, as 

 in G. (Myrmecocystis) cerebriformis (Pseudogenea californica) became an 

 entirely irregular, tortuous structure. The single hymenia are more or 

 less bent, being concave toward the central cavity of the fructification; 

 the ascus tips, therefore, lie toward the interior of the hymenophore on the 



