TILLETIA TRITICI 255 



that, when seen from above, they resemble the spores shown in 

 Figs. 124 and 125. 



Basidiospore -deposits collected on copper-sulphated slides are 

 very convenient for studying the size of the spores. One mounts 

 the spores in water under a cover-glass in the usual way. It is then 

 seen that the spores are very variable in size (cf. Figs. 124 and 125). 

 The smallest spores are 14 fi long and 3/z wide, while the largest ones 

 are about 42 //, long and 6 jx wide. Thus the largest spores are three 

 times as long as the shortest and twice as wide. For 118 spores the 

 average length was found to be 21-1 jx and the average width 

 about 4 • 5 ju,. 



The dry-needle method of making monosporous cultures from 

 basidiospores, as described by Hanna 1 for species of Coprinus and 

 other Hymenomycetes, is impracticable for the basidiospores of 

 Tilletia tritici : (1) because the spores do not survive desiccation ; 

 and (2) because the spores become so firmly attached to a glass slide 

 that, when one attempts to remove them with a needle, they are 

 torn into pieces. 



The Development and Discharge of Basidiospores in Dry 

 Air. — During the winter, when the experiments on Tilletia tritici 

 were carried out, the air in the laboratory was extremely dry, its 

 relative humidity being often only 30-35. Chlamydospores were 

 sown on plain agar in a Petri" dish and, a few days afterwards, 

 sterigmata and basidiospores were developing on the promycelia 

 in the usual way. The lid of the dish was removed and the culture, 

 exposed to the air of the laboratory, was examined with the high 

 power of the microscope. Attention was being directed to the 

 development of the basidiospores on the H -shaped pairs of sterig- 

 mata when it was noticed that, although the culture had been open 

 for half an hour, certain young basidiospores under observation 

 continued to increase in size, as though they were not affected by 

 the dry air. In order to determine whether or not basidiospores can 

 develop and be discharged in large numbers in dry air, and, if so, for 

 how long a time, the following experiment was made. A Petri-dish 

 culture containing mycelium which was producing numerous basidio- 



1 W. F. Hanna, " The Dry-needle Method of making Monosporous Cultures of Hy- 

 menomycetes and Other Fungi," Annals of Botany, Vol. XXXVIII, 1924, pp. 791-794. 



