32 James G. Horsfall 



is known of infection phenomena. Waters (1928:189) found that the 

 first uredinia appear after about eight or nine days on leaves of alsike 

 clover inoculated in petri dishes. Telia begin to form in nature about 

 October 1. Waters (1928:189) has shown recently that telia may be 

 induced experimentally by three treatments: starvation of the suscept, 

 with the later addition of a rich food supply; sudden change of the suscept 

 from a well-fed condition to a stage of starvation; and continued supply 

 of food, with a gradual dying of the suscept cells and a lowering of metab- 

 olism. The latter condition probably exists in nature, for telia of the 

 red- and alsike-clover form have not been seen before the latter part of 

 September or the first of October. Sydow and Sydow (1910:132) state, 

 however, that telia may appear on white clover from May onward. Telio- 

 spores are not greatly different morphologically from urediniospores except 

 that they are darker in color and have a slightly thicker wall. They have 

 also one germ pore, while the urediniospores have several arranged equa- 

 torially. Teliospores may be borne directly in the same sorus with the 

 urediniospores or in separate sori. The teliospores serve to carry the 

 fungus over the winter. 



Epiphytology 



Miss Howell (1890 a: 129) maintains that the clover rusts are most 

 prevalent in cool, wet seasons. If this were true, the fungus should be 

 at its height in the spring rather than in dry midsummer or after as the 

 writer has always found it. 



Control 



No actual experimental work on the control of clover rusts seems to 

 have been reported in the literature. 



Miss Howell (1890 a: 139) advocates plowing under the second crop 

 and burning over diseased fields in the autumn. These opinions found 

 subsequent expression in the writings of Pammel (1891:55) and of Free- 

 man (1905:292). Miss Howell (1890 a: 139) said that "the application 

 of fungicides seems impracticable." 



Until the work of Kightlinger (1925) most workers inclined to the view 

 that rusts could not be controlled with fungicides. Much recent work 

 has shown (Greaney, 1928) that wheat rusts may be controlled with 

 sulfur dust. The work herein reported appears to be the first dealing 

 with the control of clover rusts with fungicides. 



Effect of sulfur. The results obtained with various sulfurs are extensive 

 and seem to be rather conclusive. Data on the white-clover rust are not 

 presented since the spores germinate poorly. The data on the red-clover 

 and alsike-clover forms are given in tables 13 and 14. 



