MICHIGAN ACADEMY OF SCIENCE. 



73 



the louger. Furtheriiiore, it is completely iiidei)eii(leiit of the un- 

 inucleate stage and not (le])endent ujuju it as in the Ascomyceteae. 

 Its cells are essentially diploid for they contain two nuclei (respec- 

 tively male and female) but each nucleus is Iiaploid. The dia- 

 gram (Fig. 10) shows the stage between cell union in (he aeciura 

 (CU) and nuclear union in the teliospore (NU) as considerably 

 longer than the stage from reduction division (RD) and sporidial 

 formation to cell union (CU). 



12 



Figure 11. Sexual cycle in Tilletia. 

 Figure 12. Sexual cycle in Agaricales. 



In the genus Tilletia (Fig. 11) the binucleate stage is extended 

 to its fullest extent. Here the vegetative nn^celium for the whole 

 life history of the fungus consists of binucleate cells. At the 

 time of spore formation the young spores are binucleate but the 

 nuclei unite so that the only diploid nucleus of the life jiistory 

 is formed. A promycelium is formed and within it takes place in 

 all probability the reduction di\'ision so that the nuclei of the 

 sporidia are haploid again. The sporidia almost invariably con- 

 jugate even before becoming detached from the promycelium, the 

 nucleus from one passing into the other sporidium but Avith no 

 nuclear fusion. The germ tube from this binucleate sporidium has 

 its nuclei two to each cell. Here Ave have the three main events 

 of the sexual cycle in immediate succession, nuclear union in the 

 spore, reduction division in the promycelium and cell union in the 

 si)oridia, Avitli the whole vegetative mycelium possessing tAvo 

 nuclei to a cell. 



Finally Ave must look at the Agaricales in Avhich the point at 



