12 USTILAGO AVENAE AND USTILAGO LEVIS 



,'ii accumulation of mycelium on the surface of the cultures, young 

 : 'ecllings produced from deglumed seed were dipped into the culture so- 

 lution and thereby the sprouts and kernels were inoculated with my- 

 ( 'Hum. Roesch describes the invasion of the seedling in some detail. 

 The hyphae penetrate the epidermis and the outer layers of cells by 



.ring directly through them. In the inner tissues, however, the my- 



<• 'limn becomes intercellular. The protoplasm of the invading hyphae 



migrates with the hyphal tips and leaves empty walls behind in its path. 



Penetration was observed in the axis as well as in the coleoptile. In the 



Latter, however, the penetrating hyphae in most cases, did not enter as 



ii- as the third leaf. To determine in what stage of development the 



: 'edling is most susceptible. Roesch inoculated seedlings of different 



lengths, varying from 3 to 4 millimeters to 3 centimeters. After a pe- 



iod of three days, many relatively long hyphae were found in the 



ounger seedlings while in the older ones hyphae were very scarce. The 



.ungus seems to have the power to dissolve only the cellulose of thin cell 



alls. The susceptible stage of the young seedling expires when the first 

 I ;af breaks out of the coleoptile. 



The pathogene can penetrate such fully immune varieties of oats as 

 Av( na brevis. In these cases the hyphae grow very slowly and produce 

 ;>lasma-poor threads, possibly as a result of unfavorable growth condi- 

 ions. The pathogene may also penetrate even the seedlings of wheat, 

 barley, rye, and oat grass. Further development of the hyphae, how- 

 < ver, does not take place in these plants. With peas and beets, no pene- 

 tration was observed. 



In testing the same varieties during two different years, Roesch ob- 

 t lined no great differences in percentages of infection for the respective 

 varieties', and therefore he concludes that susceptibility or resistance is 

 ; n hereditary variety character. 



By sowing some of his oats later in the season he noted higher amounts 

 of infection. He advises, therefore, early spring sowing as a means of 

 control. 



The smaller inner grains produced higher amounts of smut, just as 

 had been noted by Arland. Roesch believes this is due to the lower vi- 

 tality of the inner grains, for he noticed that the plants developing there- 

 from grew more slowTy in their early stages. 



In several varieties of oats, Roesch also, as had Diehl, noticed consid- 

 erable variations in the degree to which the blossoms opened for polli- 

 nation. He concludes, therefore, that the possibility of inoculation is 

 thus affected. Even in the same spikelet the second and the third flower 

 open wider, and for a longer time, than the first flower. On this account 

 Roesch recommends that the small grains be eliminated from the seed. 



For the purpose of testing varieties, Roesch placed pieces of glumes 



