8 USTILAGO AVENAE AND USTILAGO LEVIS 



cient supply of moisture is necessary at the time of germination of the 

 seed and the spore. Clinton (1900: 308) is of the opinion that varying 

 amounts of moisture may have a direct effect upon the amount of infec- 

 tion. He experimented with oats sown at different depths, and found 

 that those broadcast resulted in 2 per cent of smut, those planted 1 inch 

 deep resulted in 6 per cent of smut, and those planted 4 inches deep re- 

 sulted in 10 per cent of smut. This he explains as being due in part to 

 differences in soil-moisture content at the different depths. 



At the time of spore dissemination, moisture plays an important part, 

 for it is evident that heavy rains at this time will carry a large number 

 of the spores into the soil and thus decrease the chance of inoculation. 

 On the other hand, rain may aid in lodging the spores between the 

 glumes. Jensen (1888:405) noted that oats dipped in spore-charged 

 water gave 29 per cent of smut, while those dusted with dry spores re- 

 sulted in no infection. From this it would seem logical to assume that 

 rains might tend to wash spores from the exterior of the glumes in be- 

 tween the closed glumes and the caryopsis, especially if the rains were 

 light and came after a day favorable for spore dissemination. 



THE LEIPZIG INVESTIGATIONS 

 ZADE'S STUDIES, 1922 



As has already been intimated, some of Zade's (1922) observations 

 and conclusions are not in keeping with the conception of the life history 

 of Ustilago avenae as it has just been presented. 



First of all, Zade confirmed the work of previous investigators in so 

 far as his experiments showed that spores applied to the exterior of the 

 glumes did not produce any appreciable amount of smut. He thinks, 

 however, that the spores which lodge on the kernels of those oats that 

 are deglumed during threshing, play a part in the usual percentage of 

 infection. Spores applied after the glumes were removed gave much 

 better results, but even here a maximum infection of only 26.9 per cent 

 was obtained. Zade concluded that, although spores which lodge be- 

 tween the glumes can cause infection, the degree of infection is not suf- 

 ficient to explain the frequency of epiphytotic attacks of the disease. 



When he applied spores to the blossoms of oats at pollination time and 

 subsequently examined them, Zade discovert -<l that almost all of the 

 spores which fell on the stigma began to germinate at once (in from fif- 

 teen to twenty hours, in the mild damp weather at the time of his ex- 

 periment). The promycelia formed from the spores tended to be unusu- 

 ally long, but were otherwise normal and gave rise to budding sporidia. 

 These sporidia produced hyphae which came in contact with the 

 inner epidermis of the glumes and formed mycelium in the parenchyma 

 beneath this epidermis. Zade obtained no evidence of flower infection 



