252 



RESEARCHES ON FUNGI 



in Fig. 123. It was obtained by inverting a vigorous, Petri-dish, 

 potato-dextrose-agar culture over a dry copper-sulphated glass 

 slide for several days, and it was photographed against a black 

 background. Two photomicrographs showing basidiospores from a 



less crowded spore-deposit 

 are reproduced in Figs. 124 

 and 125. 



When the basidiospores 

 fall through air which is 

 saturated with moisture or 

 nearly so, the spore-deposit 

 produced always has the 

 appearance shown in Figs. 

 124 and 125 ; but, when 

 they fall through relatively 

 dry air, the spore-deposit 

 has the appearance shown 

 in Fig. 126. Spore-deposits 

 like that shown in Fig. 126 

 can be obtained by inverting 

 either a Petri-dish or a test- 

 tube culture over a glass 

 slide in a room containing 

 dry air, with a space of 

 0* 5-1-0 cm. left between 

 the base of the glass vessel 

 and the slide (cf. Fig. 128, 

 p. 256). The air in the 

 laboratory at Winnipeg 

 during the winter is extremely dry and its relative humidity was 

 found to be 30-35. 



The spores of a spore-deposit collected in dry air, when seen 

 from above with the microscope (Fig. 126), appear as oval particles, 

 but careful focussing shows that each one exhibits two more or 

 less rounded parts closely adherent to one another. These rounded 

 parts in reality are the ends of the spores. This can easily be proved 

 by taking the glass slide to which the spores are attached, by turning 



Fig. 125. — Tilletia tritici. A photomicrograph 

 of a basidiospore-deposit collected during 

 one night on a dry glass slide from an 

 inverted Petri-dish culture. The slide 

 was not copper-sulphated, so that before 

 it was removed from the Petri dish some 

 of the spores had begun to germinate. 

 The basidiospores vary considerably in 

 size. Stained with iodine. Magnification, 

 230. 



