— 135 — 



distinct from the aecidia, continued to be produced until summer.* 

 The three spore forms also disappeared from the White Clover ; 



but later, aecidia were produced which continued to develop a 



few at a time, until summer, being accompanied during the latter 



part of the spring by uredo and teleutospores. 



Though carefully watched during the spring, the plants in the 



field showed no traces of any of the spore forms until the middle 



of May when aecidia were discovered on the White Clover. A little 



later, the other two stages appeared upon the same plants but not 



until some time had elapsed were they found upon the Red Clover. 



All three forms continued to be produced, though not abundantly, 



throughout the summer. 



From the above statements, the fact may be noticed that the 



uredo and teleutospores almost invariably followed the aecidia. 



This seemed to indicate that the aecidia gave rise to the other two 



forms but afforded no direct proof. 



ARTIFICIAL CULTURES AND INFECTIONS. 



Uredo Stage, II : Fresh, mature uredo spores germinated 

 readily at all times during the year in distilled water or a decoc- 

 tion of clover leaves properly sterilized. Care was taken to steril- 

 ize all apparatus used in making the cultures. 



A series of experiments showed that the uredo spores germinate 

 most freely and rapidly at a temperature varying from n — 16° C.f 

 Germination beginning in from i}£ to 3 hours. The lowest tem- 

 perature limit of germination lay between 7 and 1 1° C ; the high- 

 est, between 21 and 25°.^ 



Artificial infections with germinating uredo spores were made 

 upon small clover plants raised from seed sown in the fall. A 

 portion of these seeds had been sterilized in copper sulphate so- 

 lution to destroy any spores which might be attached to them. 

 No traces of the fungus appeared upon the plants produced from 

 either the sterilized or unsterilized seeds from which it may be 

 inferred that the fungus was not propagated through the germi- 



— * 



*So far as can be ascertained, the aecidiiun has never before been re- 

 ported in this country upon the Red Clover, but there seemed to be no doubt 

 that the form was identical with that on the White Clover. 



t52°— 6i° Fahr. 



\1° Centigrade = about 45 Fahr.; 25 Cent. = 77 Fahr. 



