TUBERALES 363 



phogenetic forces (unequal growth of outer and inner fructification layers 

 and consequent folding and curving of fructification wall, localization of 

 formation of asci, etc.) have been active, as in the Sphaerosoma-Choiro- 

 myces series. The significance of. the layer Ri, and consequently the 

 whole position of the series, however, is still obscure. The development 

 of Genea Thwaitesii leads one to suppose that the layer Ri is a true epithe- 

 cium, that has developed after the fraying of the parts of the outer rind 

 Ra lying above the fructification. In this sense, Genea might be con- 

 nected to the hemiangiocarpous Pezizales, particularly to the Pezizaceae. 

 After Genea, the epithecium has undergone a special development to a 

 pseudoparenchymatous cover layer which possesses no analogue in the 

 Discomycetes. Thus an explanation can only result from an ontogenetic 

 investigation of the young stages. 



