Several months ago, I observed in the Horticulturist an inquiry relative to the mildew. on Grapes, and as the subject is one of great importance, I had anticipated seeing some fight thrown upon it by some of your correspondents. I now refer to the matter again for the double purpose of recording my own ideas on the subject, and to solicit others of more experience to favor us with their views; by this means we may hope to gain information that will enable us to arrive at some definite knowledge in regard to the origin and cause of the malady. To many the inquiry may seem of little moment, since its ravages are so easily arrested, but prevention is said to be better than cure, and as the whole question of cultivating foreign Grapes in the open air rests upon their exemption from this disease, the subject becomes of vast import) and demands our serious attention.

My own experience in Grape culture leads me to the belief that the true source of this disease has not been fully recognised. It is well known that fungoid attacks are a consequence of disordered organism, and not a cause. The germs of parasite fungi are constantly present in the atmosphere, ready to develop wherever they find a proper medium. This medium is found in decomposing organic substances, and such are seized upon, although decomposition is so incipient as not to be visible to the naked eye. The question then is - what occasions this disorganism in the fruit of the Grape? The answer will show the cause of mildew. Grape cultivators appear to agree on one point, viz: that an unequal distribution of the elements of growth predisposes to mildew. Hence we find its appearance attributed to sudden fluctuations of the atmosphere from heat to cold, and the reverse, a humid atmosphere, roots in wet, cold soil, and similar conjectures. In a recent article in a horticultural journal on this subject, the writer attributes its appearance to damp, warm air suddenly brought in contact with the fruit, causing a deposition of dew. I cannot practically conceive the conditions necessary for this occurrence ever taking place in a grapery during the summer months.

Mildew is so often associated with dampness, that in the absence of practical observation such a conclusion seems very plausible. I am of opinion that in this case we must refer it to a deficiency rather than an over-supply of atmospheric moisture. LINDLEY, in his Theory of Horticulture, remarks that "mildew is often produced by a dry' air acting upon a delicate surface of vegetable tissue," and we can readily suppose that the excessive and long-continued heat of our summers would, by great and constant evaporation, weaken and tend to general debility, more especially in regard to exotics. This supposition is further strengthened by the fact that all our native Grapes have thick skins and are thus enabled to resist evaporation from their surfaces. Early forced Grapes that are ripe before the dry season, are never troubled with mildew. The Gooseberry attains greatest perfection in cool, moist climates; with us it is useless, because of the aridity of the climate. The leaves of many plants, not natives, as the English Hawthorn, Lilacs, etc, are frequently white with mildew in the hottest and dryest seasons. I have long ago satisfied myself that mildew may be prevented by judicious airing. Admitting currents of dry air to come in contact with the young fruit will certainly produce mildew.

I consider front ventilators quite unnecessary in graperies, and indeed, they could be dispensed with in green-houses, also. A few years ago it was rare to find a green-house with plants in it during summer; the general impression being that nothing but Cactuses, or such like, could live there, owing to heat and aridity. Shading and limited ventilation has now been adopted, and greenhouses invite and repay a visit in summer as well as in winter; they are now put to their legitimate use, instead of being lumber repositories the gayest part of the season.

I have no means at hand of ascertaining whether the vine mildew so prevalent of late in Europe, has its origin in aridity. It would be interesting to know whether the seasons there have been dryer than usual I recollect reading an extract from a foreign paper, where the writer in detailing the progress of the disease on his vines, incidentally remarked that "the first notice taken of the disease was about the middle of June; previous to that, the weather was excessively dry.19 His subsequent remarks, however, tended to show that he traced no relation between the dryness and the disease.

It may be necessary to observe that I do not by any means suppose that aridity is the cause of every kind of mildew. On the contrary, that is only one of many known causes, and I submit that it is the most likely in the present case.

I may state that I have gathered from open air culture, as perfect fruit of B. Hamburgh, Sweetwater, Frankenthal, and other varieties of foreign Grapes, as I ever saw in a grapery; and further, I have seen fruit beautifully ripened and colored, and bunches completely covered with mildew at the same time on the same plant: those mildewed were elevated and exposed, while the others were shaded with the foliage, and within a few inches of a box kept full of water. I could quote many examples corroborative of my views as expressed above, but will reserve them for the present.

Grape Mildew #1

We cut the following from a French publication. With reference to the use of coal tar, we would enforce great care in its application; its baneful effects on foliage are well known. Skillfully applied to the stems while the vines are defoliated'taking care to omit the buds, the remedy is with time, and may be interesting to those who are troubled with this pest:

" M. Rivet states that in 1847 he was invited by Dr. Lots to examine a sort of wine to which extraordidary properties were attributed. Another invitation to the same effect was received in 1849 from M. Souleyet, who spoke highly of the efficacy of this wine in coring some diseases. M. Rivet found iodine in the wine; and he learned that the vines which produced it were not attacked by the Oidium, and that M. Mouries had effected remarkable cures among vines by manure containing iodine. Having made some experiments, the following facte were elicited: 1st Manure produced by the fermentation of marine plants has been employed in some parts of Spain since 1835 The soil which has received this manure contains, on the average, 1-600000 part of iodine. The vines which grow in it have never, up to the present time, been attacked by the Oidium. 2nd. The wine made from these vines has some peculiar qualities. In commerce, where it is rare, it bears the name of Malaga Rives de Mer. It is of all vegetable productions the richest in iodine, containing on the average 1-50000 part of that principle. 3rd. Iodine found naturally in plants or animals possesses an action which, by its nature and intensity, cannot be produced by its chemical preparations.

M. Didot pointed out the absence of Oidium on vines, the wood of which had been smeared over with coal tar.

M. Lapierre-Beaupre stated that according to his observations the mildew does not attack the stem; the vines which were diseased in 1852 even appear to have for the most part escaped in 1853. It was stated by M. Pascal that acetate of lead prevents the development of Oidium and other cryptogams. M. Sourdette proposes a simple and inexpensive preservative, which has proved successful in some experiments made during two years in the neighborhood of Bordeaux. In order to prevent and arrest the development of the Oidium, it is sufficient, three weeks after pruning the vine, to smear the stem and shoots with pure liquid tar, applied with a large brush. This operation costs very little, and has proved very successful on ail the plants on which it has been performed, even although they were in the midst of infected vines. - Comptes Rendus.

An officer of the Navy, lately at Valparaiso, writes us: "I thought of you the other day when looking at an Araucaria Imbricata, forty feet high, which stands in the midst of a public garden here - a sort of nursery garden, in which there are many things which would please you and those of your friends who delight in trees and flowers".

Indeed it would I Our own plants have stood the late trying winter better than some others of the new Evergreens, and we confess to having some hope of naturalising this Araucaria to our midland climate.