It seems to be the mission of a large class of fungi to act the part of scavengers in Nature, as they hasten the decomposition of dead and decaying organisms, which otherwise might taint the atmosphere and breed disease. There are others again which do not subsist upon lifeless bodies, but upon those which are alive and in health; and these the cultivator has the most to dread, as they do much harm to his crops, and in some cases utterly destroy them.

Perhaps no relief from their ravages could be gained in knowing whether plants that are perfectly healthy are as liable to be attacked as those with impaired vttality; but, as the subject is an interesting one, and as much diversity of opinion exists thereon, some satisfaction would be afforded in knowing the exact state of the case.

Those who believe that disease, or, at least, a low state of vitality, invariably precedes mildew, support their views by saying that in the case of rose bushes under glass being affected it is because of currents of cold air passing through the house, too much or too little moisture in the soil or in the atmosphere, or sudden and important changes of temperature, which affect the constructive energies of the plants, thus bringing them into a fit condition to be preyed upon; all of which may be true, and no careful cultivator but will guard against all such contingencies. It seems, nevertheless, a one-sided view of a complex subject, and affords no satisfactory solution of phenomena frequently observed both in in-door and out-door culture.

Last season, and after a rather protracted period of drouth, it rained more or less for several days in succession, when quite a number of rose-bushes under glass showed unmistakable signs of mildew. But in this case the change in the weather was as favorable for the plants as it proved to be for the mildew. And I remember a somewhat similar case that occurred several years ago in a house of young grape-vines, which continued in vigorous growth from spring until August, when they were suddenly attacked by the parasite then known as Oidium Tuckerii, the result of which was, that the foliage which gave promise of performing its work satisfactorily until the close of the season, was wholly destroyed in a day or two. And, also, it must be in the recollection of many how that, some forty years ago, whole fields of potatoes in the very bloom of health were utterly destroyed in a few hours by one of the most destructive parasites of which we have any knowledge, and one which, instead of selecting as its victims plants that were weak and sickly, chose rather those that were strong and in health.

From these and similar examples no evidence can be educed in support of the very popular belief that debility must precede the attacks of fungi. On the contrary, the evidence is strong that when circumstances favor the germination of the spores, they can derive support from congenial plants whether they are in sickness or in health. And I cannot believe that spores alighting upon healthy plants will remain at rest or perish, unless adverse influences have toned them down to a state in which alone they can afford due nourishment. I believe rather that, like seeds of higher grade, these minute bodies require a combination of favoring circumstances for their development and growth, some of which seem to be, special conditions of light, heat and moisture, and when these exist mildew will show itself suddenly and before any material change can take place to weaken the plants upon which it feeds.

New Haven, Conn., Oct. 30, 1885.