22 USTILAGO AVENAE AND USTILAGO LEVIS 



Deductions 



Since the nature and position of the pathogene structures in each ease 

 is known, it is an easy matter to approximate the amounts of seedling 

 invasion due to the various pathogene structures in the seed. 



Ustilago avenai table 2). — It will be observed from lot 3, in which 

 seedling invasion was due to mycelium in or on the pericarp and possi- 

 bly some spores adhering to it. that 61.5 per cent of smutted plants re- 

 sulted, which is 91.8 per cent of the total smut obtained in lot 2. Since 

 examinations of samples of this seed showed that very few of the spores 

 had remained ungerminated, very little, indeed, of this 91.8 per cent 

 could have resulted from overwintered spores. Furthermore, when de- 

 glumed seed was dusted with spores (lot 5), in which case they received 

 exceedingly larger quantities of inoculum than could possibly have en- 

 tered the flowers in the field, a comparative percentage of only 11.8 per 

 cent of smutted plants resulted. Even this 11.8 per cent was not due 

 entirely to spores winch remained ungerminated, for it was observed 

 here, ms well ms in ail cases in which spores were applied after harvest, 

 that not only had many of them germinated in storage but penetration 

 and invasion of the pericarp also had taken place. Moreover, the 1.8 

 per cent of smutted plants resulting from spores on the outside of the 

 glumes (lot 4) confirms the already well-established conclusion that such 

 spores also play an insignificant role. 



With lot 7 of the glumeless variety, in which the smutted plants arose 

 from mycelium in or on the pericarp and possibly some spores adher- 

 ing to it. a percentage of 58.2 occurred. Here again, as was learned 

 from previous examination of seed, very few spores remained ungermi- 

 nated. and hence very little of the 58.2 per cent could have come from 

 dormant spores. Lot 8, which received greater numbers of spores than 

 would have reached the kernels in the field, contained 12.4 per cent of 

 smutted plants. 



In both the glumed and the ejlumeless oats it is very evident, then, 

 that the majority of the smutted plants were certainly due to the my- 

 celium in or on the pericarp of the seed. Overwintered spores, as well as 

 any pathogene structures in or on the glumes, play a very subordinate 

 part in seedling invasion. 



Ustilago U vis (table 3). — in lor 3, 66.2 per cent of smutted plants re- 

 - 'It d From mycelium in or on the pericarp and possibly some overwin- 

 i red spores adhering to it. This 66.2 per cent represents 98 per cent of 

 the total smut, or the 67. 5 per cent, obtained from lot 2. Since very few 

 of the spores were observed to have remained ungerminated after the 

 inoculation of the flowers, most of the 98 per cent of infection was due 

 to mycelium and not to overwintered spores. This is emphasized also by 

 the fact that when deglumed seed was dusted with spores at harvest time 



