Summary. The viability of the chlamydospores of V. avenae and U. levis has been under investigation since 1925. Samples of spores were tested dating back to 1921. The results are expressed in terms of percentage germination. Tests were carried out for the most part on 2 per cent. cane‐sugar solution or on an extract made from the pales of oats. Samples of U. levis showed a short “after ripening” period. They reached a maximum germination figure about two months after harvest and showed no loss in viability during a period of 2 to 21/2 years. Some samples were viable after 51/2 years. Panicles of U. avenae collected soon after exsertion yielded immature spores which quickly lost their viability. Mature samples, collected by covering the panicles with pollen‐proof bags, showed only a slight loss in viability after nearly 2 years in storage. The influence on viability of several methods of storage was investigated. The data emphasise the importance of maturity as a critical factor in the viability of samples. Divergent results obtained with the same species from time to time are probably to be explained by differences in the maturity and age of the samples tested. The significa
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