50 MASSACHUSETTS HORTICULTURAL SOCIETY. 



"We must remember first of all that warmth and moisture are 

 essential to the germination of these spores. In cases, then, 

 where these conditions can be controlled, as in culture under glass, 

 anything like an epidemic of mildew need never be feared. And 

 intelligent market gardeners no longer do fear the mildewing of 

 lettuce in glass houses, because they have learned how to check it 

 promptly. But in out-door culture these meteorological condi- 

 tions are only to a very limited degree controllable. It is certain 

 that the injury caused by mildews in a dry season is insignificant 

 by comparison with the loss in a wet season, and it has been found 

 in the case of the grape vine that leaves protected from dew are 

 much more rarely attacked than those exposed. This result 

 would be expected on theoretical grounds, since the spores cannot 

 germinate on a dry leaf. 



During the past few years numerous experiments have been 

 made in Europe and America in applying to grape vines various 

 substances which ma}' act as fungicides, preventing the growth of 

 the parasite without injurj^ to the leaves of the vine. For details 

 of the various preparations used and the results of their api>lica- 

 tion, reference may be had to Bulletin No. 5 of the Botanical 

 Division of the United States Department of Agriculture. It is 

 suflScient to say here that a considerable degree of success has 

 attended the use of some of the applications. The most generally 

 useful preparation seems to be that known as the "Bordeaux 

 mixture," which consists of sulphate of copper, quicklime, and 

 water, in definite proportions. This is sprayed over the plants 

 thoroughly and when it has dried there remains a compound 

 adhering to the leaves which does them no harm, but is promptly 

 fatal to fungus-spores falling on it. This mixture ought to be 

 equally eflScacious in the related diseases we have discussed. 



A comparative stud}- of the behavior of different varieties of 

 grapes, potatoes, etc., toward their respective parasites is impor- 

 tant. So far as such studies have been made, the}' indicate a 

 much greater susceptibility or predisposition to disease on the part 

 of some than of other varieties. In the case of potatoes, the thick- 

 skinned, dark varieties resist the rot much more successfully than 

 the light, thin-skinned ones, some of which seem to ofl^er a pecul- 

 iarly favorable soil for its development. 



Finally, it is a cardinal principle in dealing with any disease, 

 that a thoroughly healthy organism has the best possible chance of 



