210 ANNUAL REPORT. 



drop of water. After about an hour and a quarter the contents of the 

 spore divide up and the parts escape and swim around very rapidly 

 about fifteen minutes and then they come to rest and germinate. If 

 thej' are on the surface of a leaf where they can send out their threads 

 they will propagate the fungus, but as I say they can't live over win- 

 ter. There must be some other way and there is. This was discov- 

 ered by Prof. W. G. Farlow. 



The threads within the leaf produce thick-walled spores much larger 

 and stronger than the other kind. They are called ovspores or egg- 

 spores. They live over winter and germinate in the spring. 



You will readily see that to burn the leaves would help to destroy 

 the fungus, for the above is the only way in which it can live over 

 winter. We can never hope to burn all of them, but we can burn 

 most of the leaves of the diseased cultivated vines. The mildew 

 grows ou wild grapes as well as the cultivated ones. It is also found 

 on the Virginia Creeper. This was first discovered at Lake Minnetonka 

 by Prof. Farlow, a few 5'ears ago. It would reduce the mildew to 

 destroy the wild grapes and Vii'ginia Creeper. 



The mildew does not confine itself to the leaf but runs into the 

 berry. It probably does not originate in the berry but it goes through 

 the stem. It gives the berries a brownish appearance, but when the 

 spores are produced the berries are white. I have found them white 

 all over with spores. Prof. Trelease found that the brown, rotting 

 berries contained the fungus threads, and when kept moist spores were 

 produced, making the berry white outside. 



In Europe there is a white mold that grows on the upper surface of 

 grape leaves, known as Oidiuni TucJceri, but to what extent that occurs 

 in the United States is uncertain. It probably occurs to some extent 

 in New England. 



In this country a white mildew on the upper leaf surface is common. 

 It forms little black specks that are just large enough to be seen among 

 the white threads. Under the microscope these black specks are found 

 to contain the spores. It has been thought by some that there is a 

 connection between this and the European mildew, but the black 

 specks have never been found in Europe, and the connection is very 

 doubtful. 



Mr. Barrett. Can you tell us a remedy for these diseases? 



Prof. Seymour. Destroying the leaves, as far as possible, is the 

 best general remedy. You can't give a plant medicine, of course. 

 About the only remedy seems to be to remove the diseased parts and 



