26 (Jstilago avkxae and LFstilago levts 



vades the epidermis of the pericarp. This is true also of spores which 

 do not reach the earyopsis until threshing time. The spores arc capable 

 of immediate germination, and favorable temperature and moisture rela- 

 tions for their germination usually prevail not only in the field but also 

 in storage. 

 With Ustilago levis 



It has been pointed out that relatively Few spores of I', levis reach the 

 ovary of glumed oats at blossoming time. However, those thai do suc- 

 ceed in entering the latest blossoms to mature, behave as has been de- 

 scribed for V. avenae. 



In the glumeless varieties, the spores germinate, in all cases, shortly 

 after they have reached the ovary or the maturing earyopsis. Without 

 much doubt, this happens whenever they reach their goal while the oats 

 are still in the field. The only exception to immediate germination 

 would be cases in which exceedingly dry weather prevailed during the 

 time of threshing, and when the oats were stored under exceedingly dry 

 conditions. Examination of oats that had been dusted with spores 

 shortly after threshing and stored in paper bags under ordinary mois- 

 ture and temperature conditions prevailing in the office of the writer, 

 showed a considerable amount of germination in the following spring 

 ( Plate II, 4). These points, however, are discussed more in detail later. 



Infection studies 



Since infection was found to be more or less alike in both loose and 

 covered smut, the two processes are discussed together. 



The time at which infection begins depends upon the time of penetra- 

 tion of the epidermal cells of the pericarp. This varies, as has been 

 noted. However, the process is the same whether it begins shortly after 

 pollination or as late as storage. As has been described under incuba- 

 tion, the mycelium passes into and under the epidermal cells. Just how 

 much of this is to be included in infection it would be difficult to say, 

 as no definite point marking the end of incubation and the beginning of 

 in lection can be established because no visible effect on the suscept tis- 

 sues has been observed. 



If infected seed is examined in the spring, it is seen that the mycelium 

 appears to have developed to a considerable extent during the winter and 

 can be found abundantly under or in the epidermis of all parts of the 

 pericarp. It is evident, then, that the mycelium does not stay dormant 

 throughout all of the winter, but under favorable conditions may be 

 slowly growing and extending itself. The difference in the amount of 

 mycelium at harvest time and in the spring confirms this conclusion. 



In the spring, the mycelium thus developed in the pericarp brings 

 about invasion of the young developing seedling. Just how this takes 



