TIME AND MANNER OF INFECTION. 23 



disease. A great miinber of pycnospores are also produced about, the 

 1st of July upon the very small blasted berries. These are probably 

 the chief source of the infections which follow. The pycnospores may 

 also be found more or less abundantly durin<2: the whole season upon 

 old dead and dyinjr leaves, especially of those vines which have been 

 cut and broken. 



The ascogenous form is apparently not of very frequent occur- 

 rence. It has been collected occasionally on old leaves from June to 

 November, but, judging from the small quantity found, it does not 

 seem probable that it is a very important factor in the general dis- 

 tribution and spread of the disease. Ascospores in most pyreno- 

 mycetous fungi appear to be produced normally in late winter and 

 spring. The abnormal conditions under which the cultivated cran- 

 berry is grown — the plants being generally Hooded with water from 

 November until May — prevent the production of the fruiting forms 

 of the fungus duiing that period. We have found by laboratory ex- 

 periments that the fungus does not develop upon leaves when they are 

 kept immersed in water. Twigs with leaves from vines bearing very 

 badly scalded fruit have been kept in water in the laboratory for 

 months without any external indication of tlie development of the 

 fungus, while leaves from the same plants kejjt in moist chambers 

 developed Guignardia in abundance. In the early stages of our inves- 

 tigation various inoculation experiments were tried, both in the field 

 and in the greenhouse, using plants which were presumably free 

 from disease, judging from the external appearance of the vines and 

 berries. The results of these experiments have, however, since been 

 shown to be valueless on account of the quite general occurrence of 

 the fungus in leaves and fruit Avhich appeared normal and healthy, 

 as already pointed out. In order, therefore, to make conclusive infec- 

 tion experiments it is necessary to grow plants from seed in sterile 

 soil under conditions Avhich will prevent possible infection from any 

 source except artificial inoculation. Thus far we have been unable 

 to do this, owing to the fact that great difficulty has been experienced 

 in germinating seeds and growing satisfactory plants in the green- 

 house. From field observations made in connection with our spray- 

 ing experiments it seems very probable that infection of the young 

 leaves takes place very early in the season, soon after the water is 

 removed from the bog and as soon as the first generation of pycno- 

 spores is produced upon the old dead and fallen leaves. There are 

 also observations and facts which seem to indicate that infection of 

 the berries generally takes place when they are rather young. This 

 is self-evident of course in the case of the blasted fruit, which is 

 destroyed when it is very small. Attempts to infect mature or nearly 

 mature fruit in the laboratory have in all cases been unsuccessful. 



110 



