TILLETIA TRITICI 269 



The Spore-fall Method of Inoculating Wheat Seedlings. — The 



discovery of violent basidiospore-discharge in Tilletia tritici makes 

 it possible to place ripe discharged basidiospores upon the whole 

 or any desired part of a developing wheat seedling. The spore-fall 

 method of inoculation, as used in practice, will now be briefly described. 



An agar slope bearing an active mycelial mat at its surface is 

 inverted over about half a dozen germinating wheat grains, so that 

 these are enclosed within the mouth of the test-tube. Numerous 

 basidiospores are shot away from their sterigmata, fall down the 

 tube, and settle on the primary leaf -sheath (coleophyllum) of each 

 seedling. Here they readily germinate and produce mycelia which 

 grow over the epidermal cells. The mycelia can be clearly seen 

 when a leaf -sheath is removed from a seedling, is split in half longi- 

 tudinally, and is flattened out in a drop of water under a cover- 

 glass. Giemsa stain was found to be useful for differentiating the 

 mycelia and the host-tissue. 



The Infection of Wheat Seedlings by Secondary Basidiospores of 

 Tilletia tritici and T. laevis. — By employing the spore-fall method 

 just described, it was found possible to inoculate wheat seedlings 

 solely with secondary basidiospores and thus to obtain mature 

 plants bearing heads in which all the grains were diseased, i.e. in 

 which every grain had developed into a typical bunt-ball. 1 



In February, 1928, two series of experiments were undertaken. 

 The wheat varieties employed as host-plants were obtained from 

 the State of Washington and were known to be moderately sus- 

 ceptible to bunt. The smut species were Tilletia tritici and T. 

 laevis. The T. tritici material was obtained from the State of 

 Washington and the T. laevis from Manitoba. The chlamydospores 

 were sown on an agar medium in the usual manner ; and the 

 mycelial mats, when they had been growing for about a month, 

 were used as a source of falling secondary basidiospores. Some of 

 the experiments were made in the light, and others in the dark. 

 The wheat grains were surface -sterilised in a mercuric chloride 

 solution (1 gram mercuric chloride in 1000 cc. water) for ten minutes 



1 The earlier inoculation experiments were made at Winnipeg, but the later 

 experiments, including those of which the results are embodied in the Table on 

 p. 270, were made in the greenhouse of Macdonald College, McGill University. 



