406 Dastur. — Cytology of Tilletia Tritici, ( Bjerk. ) Wint. 
of degree. The important points in the life-history are the fusion of the 
two nuclei and the uninucleate nature of the mature spore. It is of secondary 
importance at what stage the fusion takes place ; it may be delayed until 
the development of the spore, or it may take place soon after the conjugation 
of the sporidia. In the Ustilagineae and in other Basidiomycetes there is 
indefiniteness as to the place of origin of the association of the nuclear pairs. 
Federley 1 finds in Ustilago Tragopogi pratensis , Pers., the fusion of nuclei 
taking place immediately after conjugation, and therefore he has not 
observed the binucleate stage. In U. Car bo the binucleate condition plays 
a very conspicuous part in the life-history ; but in U. maydis the uninucleate 
stage is predominant, according to Rawitscher . 2 Werth and Ludwigs 3 have 
found even the youngest spore of U ". anther arum, Fi\, to be uninucleate, but 
they do not say when the fusion takes place. 
Summary. 
The cytology of Tilletia Tritici has been studied. 
The spore, on germination, produces a single-celled sporidium. 
The nucleus from the spore passes undivided into the promycelium. 
The divisions of the nucleus do not take place at any fixed stage in the 
development of the promycelium. 
The divisions of all the daughter nuclei do not necessarily commence 
simultaneously. 
The number of nuclei is variable, but generally eight. 
The sporidia are usually eight, but they may vary from four to 
sixteen. 
The migration of the nuclei into the sporidia is delayed till the latter 
become vacuolated. 
Each sporidium has usually a single nucleus and never more 
than two. 
The conjugation of the sporidia takes place either when they are still 
attached to the promycelium or after they fall off. 
As a result of the conjugation the nucleus and part or the whole of the 
cytoplasm of one sporidium pass into the other, which then germinates 
and develops a secondary sporidium. 
The secondary sporidium is small and sickle-shaped ; it is generally ; 
uninucleate, but at times is binucleate. 
In a few cases the fusion of the conjugate nuclei has been observed in 
the secondary sporidium. 
1 Federley, H. : Die Copulation der Conidien bei Ustilago Tragopogi pratensis. Ofvers. Finsk. 
Vetensk. Soc. Forhandl., vol. xlvi, 1903-1904, p. 12. 
2 Rawitscher, F. : Beitrage zur Kenntnis der Ustilagineen. Zeitschr. Bot., vol. iv, 1912, p. 703. 
3 Werth, E., and Ludwigs, K. : Zur Sporenbildung bei Rost- und Brandpilzen. Ber. der 
Deutsch. Bot. Ges., vol. xxx, 1912, p. 524. 
