44 " A Wither Tip " 0/ Plum Trees 



Experitnent 2. 



While the experiment recorded in the preceding pages was in progress, 

 the stigma of a single flower, one of an umbel consisting of two flowers 

 on a young plum tree growing in a pot in the open, was inoculated for 

 the purpose of obtaining a photographic record of a diseased flower at 

 various stages after infection. Unfortunately a storm removed the flower 

 on the ninth day after inoculation and by that time there were no other 

 flowers available suitable for a repetition of the experiment. However, 

 three photographs were secured and these show the earlier stages of the 

 disease after inoculation of the stigma with conidia of the fungus 

 (PI. IX, Figs. 7, 8 and 9). The second flower of the umbel served as a 

 control and in the photographs is seen to the left of the infected one. 



Inoculation was effected by bringing a particle of potato bearing 

 conidial tufts into contact with the stigma as in Experiment 1, on May 14. 

 The condition of the flower on the days on which the photographs were 

 obtained was as follows : 



May 19: style of inoculated flower brown for 3 mm.; the control 

 flower showed no discoloration even of the stigma; the petals of both 

 flowers had fallen by this time (Fig. 7). 



May 21 : style of inoculated flower brown to base and the discoloration 

 had extended into the ovary (Fig. 8). 



May 23: whole of 'pistil brown, the calyx lobes wore becoming 

 withered and recurved: stamens collapsed (Fig, 9). 



(c) Inoculation of Immature Plums on Trees in the 

 Plantation. 



Experiment 1. 



The experiment was carried out on young green plums (variety 

 Victoria) at a stage when they were about 2 cm. in length, the date when 

 the inoculations were made being June 20. 



Method: conidia were removed with a sterilized scalpel from the 

 surface of a culture on steamed potato and floated on sterile water in a 

 watch-glass which had been previously passed through a flame and 

 allowed to cool. The inoculations consisted in applying with a flamed 

 platinum wire loop drops of the' water containing conidia. 



The plums were treated in one of three ways: 



(1) A drop of the conidia-containing water was applied to the stalk 

 end of the plum (junction of stalk and fruit) without injuring the fruit. 



