86 



The proof of this alternation between white cedar and sweetfern 

 as hosts for the rust, Gyninosporangium EUisii was made in 

 Arthur's laboratory at Purdue. (10) This is but one of raany 

 determinations of doubles in the rust Avorld made since de 

 Bary showed the way in 1865 by germinating teleutospores of 

 wheat rust upon leaves of barberry and vice versa. (14) In this 

 connection an amusing bit of ancient history in botany is 

 recorded in the Gardener's Chronicle of 1867. An Englishman 

 named Smith expresses doubt concerning the German de Bary's 

 conclusions. He writes: . . . "If any botanist will cause an Aecid- 

 ium-spore ... to germinate on corn . . . and produce from its 

 mycelial thread a Uredo-spore . . . the case will be proved, i.e., 

 if the said botanist can permanently preserve his specimen on 

 a microscopic slide, and send it to the British Museum for all 

 comers to examine." (55) It may be noted that in Europe the 

 term, corn, means any cereal except maize. 



The barberry is allowed to rust undisturbed in the Wheaton 

 Pines since wheat is not a commercial crop in this region. 

 Two other grains also furnish us rust. Each fall college opens in 

 time for us to find rust on leaves of late-standing corn. On the 

 leaves of these dying corn stalks it is possible to find many 

 examples of the "green island" phenomenon. (43) Even when 

 the leaves are dry and yellow the infected area around each 

 rust pustule is green. The fungus seems to serve as a water 

 reservoir and, as the host plant ages, longer life is given the 

 infected cells than those of the rest of the leaf. (49) The corn 

 leaves bear both the brown pustules of uredospores which spread 

 the infection on corn all summer and the black teleutospores 

 which, after overwintering, can complete the rust cycle on the 

 yellow-flowered Oxalis of our fields. This is another of the 

 cycles established by Arthur (8) and although rust on Oxalis is 

 of rare occurrence in the field it is easy to make the shift on 

 Oxalis weeds in the planthouse. The overwintering which the 

 teleutospores require may be effected in the ice-chest. One fall 

 the class had the further good fortune to find crown rust of oats, 

 so called because the thickened tip of each yellow teleutospore 

 suggests a crown. The oats had been harvested but, judging 

 from the condition of the volunteer tufts which had escaped 

 the sickle, the crop must have been heavily rusted. That field 

 has not again been planted to oats. I never learned whether the 



