84 



FUXGI Ais^D FUKGICIDES 



After this mycelium has developed in the leaf for 

 some time, it is ready to j^roduce its spores. Conse- 

 quently it sends out through the breathing pores, or 

 stomata of the leaf, its fruiting branches. These bear 



upon their tips small oval 

 bodies, which are tlie spores. 

 Some of these fruiting 

 branches are shown in Fig. 41. 

 The '^mildew" visible to the 

 naked eye is composed of these 

 fruiting branches and their 

 spores. It only develops under 

 certain atmospheric condi- 

 tions ; so that the mycelium 

 may exist in the aSected parts 

 of the vine for some time be- 

 fore this outward manifesta- 

 tion of its presence occurs. 

 Besides the spores above de- 

 scribed, which are jiroduced 

 during the summer season, 

 and, consequently, are called 

 summer spores, there is devel- 

 oped in autumn a different 

 class of spores, by which the fungus passes through the 

 winter. Hence, these latter are called the winter spores. 

 Treatment. — Eau Celeste is a practical and effi- 

 cient preventive of this disease. Spray first a week or 

 ten days before the vines blossom ; second, as soon as 

 the berries are well set ; and third, about three weeks 

 later. In very wet seasons it may be desirable to spray 

 a fourth time, but this is seldom done. The other cop- 

 per fungicides, especially the Bordeaux mixture, would 

 doubtless prove equally effective, but eau celeste has 

 been most generally used against this fungus, at least in 

 some of the more important grape-growing regions of 

 the country. 



FIG. 41. FRUITING BRANCHES, 

 GREATLY MAGNIFIED. 



