BIOLOGIC FORMS 13 



distance below, the epiderm. These wefts may send up a few hyphae 

 which resemble those normally producing spores. In some cases a 

 few small, abortive spores are formed, while in other cases, none are 

 produced. 



This phenomenon very closely parallels that occurring in some of 

 the resistant forms of wheat. Attention will be called to this more in 

 detail later on. It will be sufficient here to emphasize the fact that 

 rye, when inoculated with Puccinia graminis spores from rye, does not 

 show any of these dead areas (see Plate I, B), the leaves remaining 

 green and producing pustules vigorously. When the spores, however, 

 are taken from barley, infection takes place, but there is not such a per- 

 fect relationship set up between host and parasite as to enable both to 

 live and thrive for a long time. 



INOCULATIONS ON OATS 



The first attempt to infect oats with stem rust from barley failed 

 absolutely. For this reason the greatest precautions were taken to 

 furnish optimum conditions for germination of spores and develop- 

 ment of the mycelium. Of 104 leaves inoculated at various times, not 

 one produced pustules. Of this number 8 were slightly flecked, but 

 showed no tendency to form pustules. In fact, the flecks were ex- 

 tremely small and very few occurred on each leaf. In some cases 

 there was but a single fleck. These might quite easily have escaped 

 detection on some of the leaves had they not been invariably situated 

 in the inoculated area. Their position in this area indicates quite 

 strongly that they were true rust flecks. In these areas the tissues of 

 the leaves seemed to have been killed outright. However, the mycelium 

 must have been very restricted in its development since the diameter 

 of a spot never exceeded -one millimeter. 



Inoculation after the use of anesthetics 



In the first trial two pots of oats were exposed to the fumes of 

 ether for 15 minutes. Immediately after tlie exposure they were 

 inoculated with fresh spores of Puccinia graminis from barley and 

 then placed under a bell jar in a shallow pan of water. Two pots 

 were exposed to chloroform fumes for an equal length of time and 

 inoculated. At the same time 25 leaves were inoculated under normal 

 conditions, as a check. 



Of those leaves exposed to ether, 4 out of a total of 20 developed 

 slight flecks but no pustules ; neither were there any unruptured pus- 

 tules, which are commonly found when infection is not normal. Of 

 those exposed to chloroform 2 out of 19 developed pustules in 12 

 days. These pustules were very small, but were unquestionably pus- 

 tules of stem rust. A few of the leaves were so indistinctly flecked 

 that it was doubtful if they were true rust flecks. 



