TILLETIA TRITICI 253 



it so that its spore-deposit surface is in a vertical position, and by- 

 then looking at the surface with the high power of the microscope. 

 The spores which then come into view resemble those shown in 

 Fig. 127. 



What explanation can be offered for the peculiar form of the 

 basidiospores of Tilletia tritici shown in Figs. 126 and 127 ? 



It has been shown by Buller and Hanna 1 that, while falling 

 through the air, the spores of Coprinus sterquilinus rapidly dry and 

 become boat- shaped, and that every spore falls and settles with its 



Fig. 126. — Tilletia tritici. Photomicrograph of a basidio- 

 spore-deposit collected in relatively dry air (rela- 

 tive-humidity 30-35) by the method illustrated in 

 Fig. 128. The sickle-shaped basidiospores, whilst 

 falling 1 cm. through the dry air, doubled up and 

 became pyriform with their two ends (seen in the 

 photograph as glistening points) directed upwards 

 (cf. Fig. 127). 



convex side downwards and its concave side upwards. Doubtless, 

 therefore, when a sickle-shaped basidiospore of Tilletia tritici is 

 shot into the air, it falls with its convex side downwards and its 

 concave side upwards, as represented diagrammatically in Fig. 119 

 (p. 246). If the spore falls through very moist air, it retains its 

 shape, strikes the substratum with the middle of its convex side, 

 and falls over ; so that, when seen from above in a spore-deposit, it 

 appears sickle-shaped as shown in Figs. 1 24 and 125. If, on the other 

 hand, the spore falls through very dry air, it dries up in about one 

 second and, in so doing, it buckles up in the middle and its two 

 arms become appressed together, so that the spore as a whole becomes 

 1 A. H. R. Buller, Researches an Fungi, Vol. Ill, 1924, p. 277, Fig. 95. 



