i8o 



PYRENOMYCETES 



[CH. 



whether exogenous or endogenous, and in the latter case whether produced 

 in simple or compound organs. In this way three families, Peyritschiel- 

 laceae (compound endogenous), Laboulbeniaceae (simple endogenous) and 

 Ceratomycetaceae (exogenous) are distinguished. 



Fig. 145. Laboulbenia chaetophora (?). a. cell formed by binucleate 

 oogonial and trichophoric cells, X430; b. first division in ascus 

 described by FauU as the anaphase, X1510; c. nuclear division in 

 spore, showing four chromosomes, x 2800 ; after FauU. 



Since almost all our knowledge of the group is due to the brilliant work 

 of Professor Thaxter of Harvard it follows that the North American species 

 are far better known than those of other localities. Such material as he was 

 able to obtain from warmer regions proved, however, exceedingly rich in 

 representatives of the group, and it is probable that further study will show 

 them to be widely distributed. The known European species are few, and 

 only two have been identified in Great Britain. 



The systematic relations of the Laboulbeniales are not easy to deter- 

 mine. They are pretty evidently monophyletic, and are highly specialized 

 along lines dependent on their peculiar habitat. The form and develop- 

 ment of the ascus is typical of the Ascomycetes, and the Laboulbeniales 

 clearly belong to that group, though it is difficult to indicate their affinities 

 within it. 



In the Laboulbeniales the young female branch consists of four parts, 

 the initial cell of the perithecium wall, the oogonium (carpogenic cell of 

 Thaxter), the trichophoric cell and the trichogyne. These correspond pretty 

 clearly with the archicarp of other groups. The initial cell of the perithecium 

 wall constitutes a stalk-cell from which the enveloping hyphae develop. 

 The trichophoric cell should probably be included as part of the trichogyne, 

 which in this sense always consists of at least two cells. After fertilization 

 the oogonium divides to form a row of cells, which are, from below upwards. 



