George Raymond Gage 5 



glumeless oats seem to suffer more than do glumed varieties. This, how- 

 ever, has been explained by Reed (1920: 38) and others as being due to 

 a more marked susceptibility of the glumeless oats. 



Incubation 



The incubation stage is held to be largely one of inactivity, extending 

 over the period from blossoming time until shortly after the oats have 

 been sown in the spring, the seed of the suscept and the spore remaining 

 dormant together throughout the winter in storage. The spores as well 

 as the oat seed may remain viable for a long time if kept dry. Accord- 

 ing to McAlpine (1910:104), Von Liebenberg germinated the chlamy- 

 dospores at the end of seven and one-half years. 



The active stage of incubation begins shortly after the oats have been 

 sown. Moisture from the soil is absorbed by the seed and the spores 

 alike, and if temperature conditions are favorable they both germinate. 

 Kiihii (1858:48-49) experimented with wheat and the stinking-smut 

 pathogene, and came to the conclusion that penetration took place in the 

 vicinity of the root node. Wolff (1873:660-661) was of the opinion 

 that penetration could take place only through the young leaf sheath in 

 the case of Urocystis occulta on rye. Kiihn (1874:5-6) extended his 

 experiments and concluded that penetration of Ustilago carbo (the name 

 then used for the pathogenes causing both the loose smut of barley and 

 that of oats) could take place in the root node, in the first stem node, 

 and also in the internode between the two. Brefeld ( 1895 : 24-26), 

 from spraying germinating oats with sporidia grown in artificial media, 

 concluded that penetration of the axis of the young seedling is effected 

 only in very young stages, and that infection does not result when the 

 seedlings are thus inoculated after the inner leaves have pushed one 

 centimeter through the leaf sheath. Lang (1913:177-178), working 

 with serial sections, claims the infection court to be the mesocotyl. This, 

 he says, elongates to push the young seedling out of the glumes. The 

 spores germinate for the most part into germ tubes, but sporidia also are 

 sometimes formed. At the end of seven days the mesocotyl is about one- 

 half centimeter long. While the cells are still normally active the germ 

 tubes remain on its surface, but when they begin to die (the mesocotyl 

 being a short-lived strueture) the germ tubes penetrate the dying cells 

 on the surfaee and reach the healthy tissue beneath. 



Infection 



According t<> Brefeld (1895:32-37). the penetrating hyphae enter 



the seedling axis and grow directly through the 1 issues and reach the 

 growing apex of the suscept. According to Lang (1913:178-179), the 

 germ tubes, upon reaching the Living cells inside of the dying mesocotyl. 



