220 GRASSES OF IOWA. 



bodies, the conidia, but under more favorable conditions of 

 food these may branch and bear secondary conidia. If the 

 nutrient material is not exhausted this process of budding may 

 be continued for a long time. These spores may propagate in 

 a decoction of manure. It will then be seen that these budding 

 conidia may be a center of infection. 



The conidia as well as the secondary conidia are blown 

 about by the wind and under proper conditions cause the infec- 

 tion of the corn plant. Several years ago Mr. F. C. Stewart* 

 made some extended studies of the germination of CDrnsmutin 

 which it was shown that the thermal death point of smut spores 

 is ISmin., 105''-106S C. in dry oven, and 52'^ C. when immersed 

 in water; and that corn is unable to come through an inch of 

 soil after 15 minutes treatment with water at 70.5" C, and in 

 dry oven at 78° C. Brefeldf found that smut spores produced 

 an abundance of secondary conidia when they were germinated 

 in sugar solution, but with us this has never been a very satis- 

 factory method of propogating them as the cultures soon 

 became infected with bacteria which materially checked the 

 progress of the germination of spores. These bacteria came 

 from the smut. 



Age has something to do with the germination of the spores. 

 In our own work fresh spores never germinated as well as those 

 perfectly dry. Those of a previous season always germinated 

 well. They may preserve their vitality for a considerable 

 length of time. Brefeld has shown that spores 2 years old 

 germinated readily, and that spores 7 years old germinated in 

 nutrient solution in from five to eight days. 



Norton and Hitchcock, however, foundthat the young spores 

 just formed germinate best, and grow more vigorously after 

 germination. Brefeld, however, found that old spores when 

 germinated will grow as vigorously as the newer. 



Manner of infection. — Until the exhaustive researches of 

 Brefeld, the statement of Kuehn,J. an excellent observer and 

 investigator were accepted. Kuehn stated that the mycelium 

 from the germinating spores enters at the root node, the most 

 tender part of the corn plant, as in the case of wheat bunt. He 

 supposed this to be true of other smuts as well. It has been 



•Effects of heat on the germination of corn and smut. Iowa Acad. Sci 2:74-78. 

 1894. 



+Untersuchungen aus dem Gesammtgebiete der Mykologle. Ueber Hefenpilze, V 

 Heft. 67-76. 1883. 



4:Bot. Zelt. 33: 123. 



