﻿Dodge: Effect of host on Gymnosporangium 525 



infection, most of the succeeding experiments were carried out 

 to check up the first results. 



It is probable that no importance need be attached to the 

 results obtained in numbers 200 and 22 1 . Only one leaf on each 

 apple seedling was infected, and this might have been due to the 

 presence in the greenhouse of young red cedars bearing G. macropus 

 and G. glohosum. No aecidia developed on these leaves. Farlow 

 (3) and Seymour (19) report Roestelia transformans on the culti- 

 vated apple. The pear and hawthorn were not infected, but as 

 only one or two plants were tested these results are also inconclusive. 



The table shows that about 50 per cent, of the Aronias were 

 infected. Three different species were employed and all gave 

 positive results. Aecidia matured on certain plants of A. arhuti- 

 folia and A. nigra, but the fungus on A. atropurpurea did not 

 develop further than the formation of the large primary hyper- 



The interval between inoculation and the first appearance of 

 the discoloration indicating infection varies from ten to fifteen 

 days. The areas on the Aronia are not especially characteristic. 

 They become raised or convexed and are frequently four or five 

 millimeters in diameter (Fig. 3). After some days, ten to twenty, 

 the parts attacked become sunken as the hypertrophies develop 

 into bright green swellings directly beneath the pits. The galls 

 sometimes seem to be three or four millimeters thick, but this 

 apparent thickness is due in part to the pit in the upper surface 

 of the leaf. 



The horn-like processes of the galls (Fig. 4) begin to grow out a 

 week or two later, after which the aecidia quickly develop and 

 reach maturity within two months after inoculation. Frequently 

 the development does not proceed further than the formation 

 of the basal galls. The leaf remains in this condition for several 

 weeks and new spermogonia are formed continually on the galls. 

 Normally aecidia are matured whenever the cornute galls are 

 developed. 



Figs. 7 and 8 show a case in which the growing point of a twig 

 has been entirely transformed by the fungus. Eight weeks elasped 

 between the taking of the photographs. 



Occasionally infected leaves curl up soon after spermogonia 



