148 DISEASES OF CULTIVATED PLANTS 



winter- fruits, which are more or less embedded in the felt of 

 mycelium, which can be removed as a film from its support. 

 During the autumn considerable numbers of the perithecia or 

 winter-fruit fall to the ground, and constitute a source of 

 danger the following season. On the other hand the dusky 

 brown mycelium, with many perithecia, remains on the shoots 

 until the following season, when the ascospores germinate 

 and infect the young leaves and fruit. In many instances 

 when a shoot appears to be perfectly free from disease, a 

 careful examination reveals the presence of minute portions 

 of mycelium located between the buds and the shoot, and I 

 suspect that this mycelium lurking in the axils of the buds 

 plays the part of resting mycelium, and gives origin to the 

 disease the following season, but I have no direct evidence 

 on this point. Resting mycelium of this nature is stated to 

 start the apple-tree mildew, an allied fungus. The European 

 gooseberry mildew ( Microsphaera grossulariae) is also very 

 common on gooseberry leaves, rarely passing on to the fruit, 

 and in the white conidial condition closely resembles that of 

 the American mildew in its young, white stage, and it is only 

 by carefully conducted microscopic work that the two can be 

 accurately distinguished. In the conidia of the American 

 mildew, certain discoid, cone-shaped, or rod-shaped bodies 

 are present (see fig. of conidia), whereas in the conidia of the 

 European mildew no such bodies are present. The widely 

 different tips of the appendages of the perithecia at once 

 distinguish between the winter fruit of the two species 

 (see figs. ). 



The bulk of English literature dealing with the subject of 

 American gooseberry mildew is perhaps more interesting from 

 a psychological than from a pathological standpoint. 



Mycelium persistent, forming compact, telly wefts, changing 

 from white to a dingy brown colour ; perithecia gregarious, 

 partly immersed in the weft of mycelium, appendages usually 

 few, coloured, short, and usually crooked ; ascus subglobose, 

 spores, 20-25X12-15/1. 



As no part of the mycelium of the fungus persists through- 

 out the winter in the tissu.s of the gooseberry plant, il is 

 evident that the appearance of the disease in the spring 

 depends entirely on infection from some outside source. The 

 bulk of such infection results from the presence of wintei 

 fruit that remains on the shoots throughout the winter. In 

 this country, excepting the fruit, the mildew is mainly con- 



