﻿Dodge: Effect of host on Gymnosporangium 535 



sowings were made just as the first leaves were opening. When 

 the last trials were made, May i6, there were still a few new leaves 

 on each plant, but most of the leaves were too old perhaps to be 

 susceptible to any rust. In order to determine this point G. 

 fraternum was sowed on nine of the plants the same day (see 

 Table IV) and three infections were obtained. 



The variable length of time required for the development of the 

 spermogonia demands that the plants should be kept under control 

 conditions for at least a month. Arthur (2) reports sowing G. 

 hiseptatum on Amelanchier canadensis which did not develop 

 spermogonia until after a period of twenty-five days. One of my 

 cultures, No. 540, required thirty days. This was a shrub of A. 

 intermedia about two feet high, which was transplanted from the 

 garden April 28, after its leaves were full grown. G. hiseptatum 

 was sown on it April 30. The plant did not do well after it 

 was transplanted; the leaves assumed what gardeners call the 

 "sleepy condition." As no spermogonia were visible May 15, the 

 plant was topped to save it. The remaining leaves soon regained 

 their normal rigidity. On May 30 spermogonia began to appear in 

 considerable numbers. Twenty-seven other infections were ob- 

 tained on Amelanchier. Six showed signs of infection on the 

 seventh day; four required eight days; ten showed in nine days; 

 six in ten days; the one infected in the garden required thirteen 

 days. The average incubation time of G. fraternum on Aronia 

 and Amelanchier appears to be between nine and twelve days. 

 Table VI contains a summary of these periods in some sixty 

 experiments with G. fraternum. 



TABLE VI 



Gymnosporangium hiseptatum (caulicolous form) 

 Amelanchier readily, but if it ever infects Aronia it i 

 under different conditions from those prevailing in 

 with the ninety-five attempts which I have made to bring it about. 



