TILLETIA TRITICI 241 



together, and so give rise to a diploid mycelium which may produce 

 chlamydospores. 



The fact that a primary basidiospore contains two nuclei, one ( +) 

 and one ( — ), and that a secondary basidiospore contains only one 

 nucleus, ( -f) or ( — ), must be of considerable importance in respect 

 to the infection of host plants and the production of bunt balls. 

 One would expect that, if primary basidiospores, which are bisexual, 

 were sown on a host-plant, diploid bunt balls would be produced ; 

 and one would also expect that, if one host-plant were inoculated 

 with ( +) secondary basidiospores only, a second with ( — ) secondary 

 basidiospores only, and a third with both (+) and ( — ) secondary 

 basidiospores (or mycelia derived from them), bunt balls would 

 appear on the third plant but not on the first two. 



The ideas, based on cytological facts, which have just been 

 suggested, find a strong support in the phytopathological work of 

 Hanna * who has observed : (1) that primary basidiospores allowed 

 to fall on wheat seedlings give subsequently a good crop of bunted 

 heads; (2) that (+) secondary basidiospores, or mycelia derived 

 from them, give no bunted heads ; (3) that ( — ) secondary basidio- 

 spores, or mycelia derived from them, give no bunted heads ; and 

 (4) that mixed (+) and ( — ) secondary basidiospores, or mycelia 

 derived from them, give bunted heads. 



In a diploid mycelium which has been formed in a host-plant, 

 the nuclei are associated in conjugate pairs and, during conjugate 

 nuclear division, clamp-connexions 2 are formed. Finally, in a 

 young chlamydospore the two nuclei of a conjugate pair fuse 

 together. 



The existence of one nucleus only in secondary basidiospores 

 has been observed by one of us (T.C.V.) in Tilletia tritici, T. laevis, 

 and T. horrida ; and Hanna 3 has found no more than a single 

 nucleus in the secondary basidiospores of Entyloma menispermi. 

 By the spore-fall method, shortly to be described, Vanterpool and 

 Hanna had no difficulty in collecting good spore-deposits of secondary 



1 W. F. Hanna, Dominion Rust Research Laboratory, personal communication. 



2 R. Seyfert, " Uber Schnallenbildung im Paarmyzel der Brandpilze," Zeitschrift 

 f. Botanik, Vol. XII, 1927, pp. 577-601. 



3 W. F. Hanna, Dominion Rust Research Laboratory, personal communication. 

 vol. v. R 



