﻿522 Dodge: Effect of host on Gymnosporangium 



On April 29, 191 1, I accompanied Dr. F. D. Kern (see Arthur, 

 la) to Newfield, New Jersey, where we found a few specimens of 

 Gymnosporangium fraternum in Hoi ton's swamp, and also a 

 quantity of G. biseptatum* Visits made to Newfield and Lake- 

 hurst at various times since have afforded opportunity for further 

 study of this stage of the rust. 



During the first week in January the most careful inspection of 

 several small marked cedars in the field failed to disclose any posi- 

 tive evidence of infection. Some of the leaves were slightly dis- 

 colored or bore yellowish spots which contained what appeared to 

 be a resinous substance but no spores. By the middle of March 

 there were many leaves which were of a light waxy-yellow color 

 throughout, and occasionally one could find, with the aid of a lens, 

 lines of eruption from which teleutospores were just emerging. 

 Sori were fully developed by the second week in April. The dis- 

 coloration of the entire leaf seems to be confined to those which 

 later bear very large sori. Where the sorus is comparatively 

 small (Plate 28, fig. i) the unoccupied parts of the leaf remain 

 green. Infected leaves die off after the sori have disappeared 

 through gelatinization. On June i, 1914, it was not difficult to 

 find sori, but they showed that in spite of the fact that it had been 

 a very dry season, they had been previously swollen. Spores from 

 these sori gave a low percentage of germination. 



Greenhouse cultures, described later, indicate that the develop- 

 ment of the sori can be hastened by at least two months. On the 

 other hand, if small cedars are brought in from nature in the last 

 week of March the "forcing process" is not especially effective. 

 The same is true for G. biseptatum. Living branches with the 

 fusiform swelUngs were obtained from Newfield March 21 and 

 kept well watered and sprinkled. The first spores available for 

 inoculation were ready April 13. At this time in nature their 

 condition was much more satisfactory. 



There is a great amount of variation in the shape, size, and the 

 thickness of the walls of the spores of the foliicolous form. I have 



