518 



distorted forms of the Oidium were clearly seen, showing the destruc- 

 tive action of these substances on fungus germs. 



I next placed the dust of roll sulphur on Oidium spores, and also the 

 dust of the flowers of sulphur on a second lot, each set being secured on 

 glass slides, an inch and a half wide by six inches long. 

 •^ These slides were subjected to moisture and heat, as before, in sepa- 

 rate jars. After the usual exposure it was observed that the same 

 fungus forms of group B appeared on the germinating Oidium. 



These results were not expected, as it has been generally supposed 

 that sulphur is a perfect preventive of fungoid growth. This led me 

 to test the effectiveness of sulphur for that purj)ose. I placed in an 

 eight-ounce jar four ounces of pure water, one ounce of green peach- 

 leaves, and two ounces of the flowers of sulphur, and subjected the whole 

 to a temperature of 75° to 80° F. In three days fermentation commenced 

 in full force, giving off a strong odor of sulphareted hydrogen. In the 

 course of ten days the leaves were completely destroyed by the fermen- 

 tation, demonstrating that, if the flowers of sulphur are anti-fungoid, the 

 beneficial results of its application have not been due, as has been sup- 

 posed, to its chemical qualities, but, probably, to its absorption of moist- 

 ure. 



These experiments also go to show that the vine fungus is a true para- 

 site, and that it will not fruit when removed from the plant on which it 

 grows. A peculiar condition of the atmosphere may also be necessary. 

 The Oidium form of the fungus is not supposed by mycologists to be a 

 true mold, but merely a condition of a species of Erysiphe. Group B 

 represents a theoretical view of its supposed condition ; 12, 13 and 14, 

 its stages of fruiting. Figs. 14 and 15 are filled with little sacs contain- 

 ing sporidia which germinate. Fig. 16, group D, represents one of 

 them, and 17 a branch of mycelium growing from them on which grows 

 the Oidium. 



It is stated on good authority that the fruit of this fungus has not 

 been seen on the vine in Europe. In the fall and summer of 1871 and 

 also 1872 I found specimens of its perfect fruit in great profusion on the 

 foreign vine of the grapery of the Department. During the last two 

 years, 1873 and 1874, not a single specimen of fruit could be found. 

 Late in the fall of 1872 Mr. William Saunders, superintendent of the ex- 

 perimental gardens, had all the branches of the foreign vines in the 

 grapery painted with a mixture of clay and carbolic acid, for the pur- 

 pose of destroying the fruit of the vine fungus. Future observations 

 may show that such treatment will prevent, in a measure, the ravages 

 of the vine fungus. It has long been observed that very dry seasons 

 are favorable to the growtli of the Erysiphe fungus. Although a hundred 

 foreign vines were exposed to the Oidium in the same grapery, very few 

 were affected by it during the last season ; and it is observed that the 

 mildew is confined to certain varieties. The black Hamburgh, for exam- 

 ple, was not affected at all by it, although growing side by side with 

 mildewed vines. The green wood is always more injured by the Oidium 

 than the ripe; consequently, as some varieties of vines ripen sooner 

 than others under the same conditions, so the green branches of the 

 later varieties will probably be more affected than those of the early. 

 It was shown by my paper on the fungus of the American grape-vine, 

 in the Annual Eeport of the Department for 1871, that the early spring 

 leaves of American grape-vines are not affected by the mildew {Perono- 

 spora viticola) during the summer months, under ordinary conditions, 

 although the leaves that sprout in summer, particularly during rainy 

 weather, when sappy and of a very light-green color, are very liable 

 to be affected with the mildew, particularly some varieties. 



