ity 
464 
tion, but doubts whether complete removal can be effected in this way 
He therefore recommended to the Academy of Sciences of Paris that a 
member of the medical section be requested to determine whether this 
substance, so poisouous to plants, is perfectly harmless to animals. M. 
Cl. Bernard was requested to perform this duty. 
MICROSCOPIC OBSERVATIONS. 
By Tuomas Taytor, MICROSCOPIST. 
The following communication was addressed to the Commissioner of 
Agriculture, the 7th of September last, by the editor of the Cultivator 
and Country Gentleman : 
Sir: The very general prevalence of grape mildew and rot, this seasen, gives in- 
creased importance to the questions which have so long perplexed practical grape- 
growers, viz: What is mildew? how many kinds of it are there? is the rot a distinct 
disease, or only a form of mildew? how is mildew propagated? what circumstances. 
of soil, climate, or culture tend to favor its propagation ? ? and what means, if any, can 
be relied on as a preventive of the evil? bs . 
Mr. Taylor, the Microscopist of the Department of Agriculture, performed a number 
of experiments with the spores of Oidium Tuckeri (the fungus of the foreign grape- 
vine) showing the facility with which they germinated when placed under cover of 
glass, with the requisite heat and moisture. He has also tested the effects of the flow- 
ers of sulphur, the vapors of turpentine, benzine, and carbolic acid, as preventives of 
the germination of thespores. In these experiments, the sulphur did not seem to have 
the effect usually ascribed to it, but the other articles entirely prevented the germina- 
tion, and evidently destroyed the vitality of the spores. This result is a little sur- 
prising as regards the sulphur, since this substance has always been relied on as the 
surest preventive of mildew in graperies. I shoald be glad if the Microscopist would 
have the kindness to state whether these experiments have been repeated, or any. 
cause discovered for the seeming anomaly. 
In reply to these inquiries, | would say that mildew is now admitted 
to be a cryptogawic plant, belonging to a low order of fungi. Some 
mycologists affirm that there are as many as eighteen species which are 
injurious to the grape-vine. Two very distinet genera are especially 
noticeable, the Hrysiphe and Peronospora. The former is principally 
confined to the foreign grape-vine, and the latter to the native. These 
two genera include most of the species of fungi which injure the grape- 
vine. Their modes of fructification, however, are different. In the 
Brysiphe, the germ-cells, which are called sporidia, are produced in 
cysts. These cysts are known by different names, as sporangia, ascl, 
or thece. This genus belongs to the Sporidiifera, the second of the 
two grand divisions into which fungi are divided. Sometimes late in 
the fall, Lrysiphe appears on the old leaves of the native grape-vine. 
Another species, quite similar in form, is found on the willow, and 
known as Erysiphe adunca, Schlecht; and still another on the maple, 
Erysiphe bicornis, Link, having eight spores. I have never found Hry- 
siphe on the young leaves of the native grape-vine. During the sum- 
mer of 1871 and of 1872, the foreign vines of the Department grapery 
were infested by immense numbers of a species of Hrysiphe. The spo- 
rangia had waving appendicles, but their terminal points were not 
hooked. Very dry and warm conditions of the atmosphere are favor- 
able to the growth of the fungus Hrysiphe, especially when graperies are 
imperfectly ventilated. 
The second genus mentioned, Peronospora, belongs to the other grand 
division of fungi, called Sporifera. The spores, which occupy the same 
position and perform functions similar to the seeds of the higher orders 
