George Raymond Gage 33 



Since some glumes are broken off by threshing, inoculation may take 

 place to a certain degree at that time. With glumeless oats the inocula- 

 tion period extends from pollination time until and during threshing. 



4. The success of inoculation is dependent to a large extent upon the 

 time of spore dissemination and the length of the period during which 

 the spores may reach the ovaries or the caryopses. U. avenae spores are 

 disseminated over a period extending from shortly before pollination 

 until harvest. They must reach the ovaries of glumed varieties of oats 

 during the time when the flowers are open for pollination, but may lodge 

 upon the ovaries or the caryopses of glumeless varieties at any time after 

 the flowers have opened. U. levis spores are not disseminated to any 

 great extent until the very last of the flowers are being pollinated. With 

 glumed varieties the possibility of the spores entering open flowers is 

 very much less than for TJ. avenae spores. With glumeless varieties the 

 majority of V. levis spores reach the caryopses of the oats during thresh- 

 ing. 



5. Mycelium resulting from the spores germinating at blossom time 

 may penetrate the glumes, but this mycelium is insignificant or at least 

 unnecessary as a source of inoculum for seedling invasion, being entirely 

 wanting in the ease of glumeless oats. 



6. Mycelium resulting from spore germination during the blossom- 

 ing period or the maturing period of the oat, or even when the oats are 

 in storage, penetrates and invades the pericarp of the caryopses and be- 

 comes established in and under the epidermal cells. 



7. The mycelium in the pericarp is accountable for most of the seed- 

 ling invasion. 



8. The success of invasion resulting in spore formation (smutted 

 spikelets) is dependent upon certain combinations of environmental fac- 

 tors, rather than on any specific one. In general, slow germination of 

 the oat and continued slow development of the plant favors the patho- 

 genes. Rapid germination and rapid growth of the plant, although they 

 do not prevent seedling invasion and infection of the lower part of the 

 plant, will often result in normal production of flowers. 



REFERENCES CITED 



Arlaxd, Anton. Der Hafer-Flugbrand, Ustilago avenae (Pers.) Jens. 



Biologische Untersuehungen mil besonderer Beriicksichtignng der 



Infektions- und Anfalligkeitsfrage. Bot. Arch. 7 : 70-111. 1924. 

 Bartholomew, Lr< n.u; K., and Jones, Edith Seymour. Relation of 



certain soil factors to the infection of oats by loose smut. Journ. 



agr. research 24 : 569-575. 1923. 



Brefeld, Oscar. Die Brandpilze II. Untersuch. Gesammtgeb. Mykol. 

 11:1-98. 1895. 



