35 



THE INFECTION OF OATS. 



.^ tliird form of loose smut must now be considered in connection with those of wheat 

 and liarley, that is, of the Hordeaceae. This is the one appearing on oats; that is, on the 

 Avenaccae. Externally this smut resembles the earlier forms in its spore masses and the form 

 of the spores. When cultivated in nutrient solution, however, these smut spores soon show great 

 differences. The loose smut of oats does not germinate sterilely, but fructiftcatively^. Conidia 

 of a definite form are formed from the hemibasidia by direct budding; these form a highly 

 characteristic species of bud conidia, the broken-down members of which grow out at once to 

 strong, long germinating tubes'-, when the nutrient solution has been exhausted. These tubes 

 will penetrate into the host plants. To the difference in germination is added now a second 

 difference, that of the period of germination of the spores. This does not end, as in the two 

 other forms, with the lapse of a year. It continues for several years and the spores, investi- 

 gated then as to their germinating strength, germinate just as strongly as those freshly gathered. 



It is evident that in this smut form we are concerned with spores which, by the energy 

 of their development and the unceasing increase of their conidia in saprophytic substrata, show 

 a power of infection not possessed by the loose smut of wheat or of barley. The latter depend 

 for their infection on young blossoms ; that is, stigma and ovule, and have been proved ineffective 

 for the inoculation of young germinating seedlings in the soil. The behaviour of the oat smut 

 takes the opposite course of action ; namely, the inoculation of young germinating seedlings, 

 which is considerablv favored by the increase of the germs of infection in the earth. 



Inoculations made earlier with loose smut of oats and reported in detail in Part XI of 

 this work-', have shown that undoubtedly the infection of young germinating seedlings takes 

 place here. The effect of the germs of infection sprayed on the young germinating seedling 

 with an atomizer showed that no total infection was obtained by these circumstances, — needing 

 closer investigation, — but only a result of from 7-20% of smutted plants. The experiments, 

 however, with infected compost and with humus soil, mixed with one-half its amount of horse 

 manure and used for covering the seed grain, gave a percentage of smutted plants which had 

 been increased up to 30-40%. 



The results obtained previously were repeated in numerous experiments made in success- 

 ive years, and particularly in the last five. They furnished no better results from inoculation 

 with the atomizer, but in experiments with humus soil and manured garden earth, they increased 

 to more than 60%. A number of subordinate circumstances are present here which favor infec- 

 tion, among them especially the longer development of the germs of infection in "the humus 

 soil and manured garden earth here used for covering the seed. Probably a delayed develop- 

 ment in the germination of the seed is here beneficial to the germs of infection. But investi- 



(1) See plate II, Part V of this work. 



(2) See plate III, Part V of this work. 



(3) 1. u. page 23. 



