238 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the same mycelial filament, in others from distant ones." Three out of 

 the seven figures of this species are distinctly homothallic in character, 

 and thus oppose the cultural evidence which alone would strongly suggest 

 a heterothallic condition. 



Pilaira anomala (Cesati) Schroter. 



Van Tieghem ('75) found the zygospores only in two cell cultures, in 

 one of which three spores were sown and in the other five. According 

 to the account given the zygospores form from " twt» flexuous branches 

 arising from the same lateral branch or from different lateral branches 

 which cross." The zygospores occurred in a cell under favorable con- 

 ditions for observation, and van Tieghem's description of the origin of the 

 zygophores would make the species homothallic. The fact that in all 

 other cell and gross cultures he never obtained zygospores, added to the 

 fact that where they were found more than one spore was sown, renders 

 the thallic condition a matter of uncertainty. 



Brefeld ('81) found zygospores only once, and on horse dung, where the 

 sporangia were luxuriantly developed. Not more than about fifty zygo- 

 spores were found, and in cultures from the sporangial spores there were 

 no more zygospores produced. The same was true of sporangial sowings 

 from germinated zygospores. The figures are negative as regards the 

 origin of the zygophores with the possible exception of Figure 27, which 

 seems to make the suspensors connect with the same hypha. 



Pilobolus crystallinus (Wiggers) Tode. 



Zopf ('88) attempted to induce the formation of zygospores by varying 

 the substratum, and used for tliis purpose both solid and liquid media, but 

 obtained negative results. Sterilized ('' ausgekochter ") horse dung was 

 placed in a crystallizing dish and inoculated with pure spore material. 

 The Pilobolus at first developed normally, but later was attacked by 

 Photrachelus fulgens and an undetermined Syncephalis. Zygospores 

 here appeared in abundance, and Zopf concludes that they were caused 

 by the suppression of the formation of sporangia resulting from the 

 attacks of these parasites. In proof of this, the following experiments 

 were made. The spores from sporangia caught pure were sown on 

 sterilized horse dung and gave rise to sporangia alone. Another similar 

 culture was infected with parasites by strewing on it fragments of dung 

 from the original diseased culture. Sporangial formation was checked 

 and zygospores appeared in abundance. It is stated (p. 356) : " In Plate 



