WHITK-PIXE BLISTER RUST. 



61 



currant plants which had been pre\'iously set out in an isolated garden for the pur- 

 pose. After inoculation the plants were covered for two days by a box ha\dng a glass 

 lid. In all cases, water was sprinkled three or four times daily on the plants and 

 on the inside of the box, to keep a high humidity. Unfortunately, during the whole 

 of the period covered by this series of inoculation the weather was exceedingly hot 

 and dry, and it was evident from a study of field conditions that infections could take 

 place at this time only with the greatest difficulty. The adverse nature of the weather 

 conditions will serve to explain the meager results. . . . 



The only positive result from this experiment ^^as that the spores would retain 

 their power of infection for a period of nine days at least; but so many failures oc- 

 curred all through the course of the work that this period can not he regarded as 

 establishing a maximum limit of life. 



It is interesting to note that the spores kept outside undenvent a complete decolori- 

 zation in two days, whereas those stored in the laboratory retained their normal 

 color, with but little change throughout the whole time of the experiment. 



The inconclusive results obtained fi'om the first set of inoculations in the field led 

 toanother later attempt with plants kept in the laboratory, for this purpose a number 

 of small plants being used from which the leaves had been stripped, so as to induce 

 the formation of secondary foliage. The methods employed in this case were the 

 same as for the first set, exept that after inoculation the shoots were kept covered 

 and moistened for the usual 48 hours inside large glass jars. (See Table IV.) 



Table IV. — Inoculation of currants with urcdospores of different ages. 



Series. 



Age of 

 spores 



(days). 



T 



2 

 4 



7 

 8 

 11 

 13 

 18 

 24 

 27 

 31 



II 



Ill 



IV 



V 



VI 



VII 



VIII ■ ... 



IX ... 



X 





Date Of inoculation, Numb«^ 

 l^l*^- used. 



August 31 



Sppteniher2 j 



September 5 i 



Septemlier fi t 



September 9 



Septemlier 11 



September 16 



September 22 



September 25 



September 29 



Date of examina- 

 tion, 1916. 



September 19 

 September 22 

 September 2.5 

 September 26 

 September 29 



October 1 



October 6 



October 12... 

 October 15... 

 October 19... 



Result. 



5 pustules on 2 leaves. 

 67 pustules on 11 leaves. 

 No infection. 

 10 pustules on 5 leaves. 

 8 pustules on 2 leaves. 

 2 pustules on 2 leaves. 

 No infection. 



Do. 



Do. 



Do. 



The results from these inoculations were somewhat better than those from the first 

 set; infections were obtained from spores kept for 13 days after collection, as showTi 

 in the tabulated record. It is still thought that this period is far below the maximum 

 period for which the spores will retain their vitality. 



In 1917 Gravatt and Taylor made a series of tests of urediniospores 

 together with seciospores and teHospores. (See p. 38 for detaUs 

 of the experiment.) They were tested weekly beginning May 8. 

 June 16 gave the last germination in lot A, while lot B persisted 

 until July 2. Although germination persisted longer in lot B, it 

 weakened decidedly somewhat earlier and was j^oorcr practically 

 throughout the test. (See Table II, p. 38.) 



In 1918, Duff (30) experimented on the longovily of urediniospores 

 placed in a refrigerator at 2° to 5° C. two weeks after collection and 

 tested in hanging drops of distilled water. He states that when 

 placed in the refrigerator — 



A negligible percentage of spores were gerrainable, but reduction in temperatiu'e 

 stimulated them to greatlv increased 'j;erniination. Bv this means a continuallv 



