musty odor which the vine exhales is nothing else than the oïdium itself; the gray color noticed on the parts attacked, after a while, is owing to the state of old age of the mushroom; the black spots which appear along the shoots, leaves, and grapes are the indelible traces of alterations its presence on the surface has produced, and which remain after its death and disappearance. The stunting of the shoots and of the grapes, the curling up and premature fall of the leaves, the development of inter-leaves, are the consequences of the profound and long-continued disturbance which the oïdium has carried into the vegetation of the vine, a disturbance whose manifestation dates from its appearance upon it. In fine, the injuries (lésions) to be seen on the grapes, the cracking and drying of the berries, are the consequences of the alterations to which the exterior of their tissue has been subjected: they cause it to lose its elasticity, and to rupture when the interior parts come to grow. THE OÏDIUM TUCKERI. The Oidium Tuckeri is a microscopic cryptogam strongly resembling the érysephes, little mushroom parasites of the most dangerous species. It is itself, then, nothing but a parasite, which feeds at the expense of the very substance of the green parts of the different organs of the vine on which it plants itself, and thus prevents their development. Down to this time it has not been observed any where else than on the vine, and does not develop itself on other plants. The cryptogam observed on various fruit-trees, on hops, on the bind-weed, and rose-bushes, are all different from the oïdium or érysephe of the vine, although their structure may be analogous to it. It is composed, 1. Of creeping filaments, very loose, performing the functions of roots (Fig. 2, m, m); they are very numerous, elongated, ramified, without cells, covering with an inextricable net-work the plant attacked.. They are provided with globular protuberances, which penetrate the outer covering of the tissue, and serve as anchors to hold on by (Fig. 2, c, c). These last, by degrees, form about them the black spots noticed on the shoots, leaves, and fruit. This assemblage of creeping filaments is designated by the term mycelium. 2. Erect filaments, divided from distance to distance into cells, and club-shaped. The cells are susceptible of being transformed each into a particular kind of seed. These filaments are designated as tigelles, or fertile filaments, in contradistinction to those of the mycelium, which are designated by the name of sterile filaments. 3. Of spores or sporules (Figs. 2 and 3, 8, 8, s); these are elipsoid corpuscles, that is to say, about the form of an egg, engendered by the cells of the tigelles, borne by them, and placed end to end at their extremities. These spores perform the function of seeds of the mushroom parasite; they germinate and reproduce it in all its parts. Thus the oïdium is furnished with distinct organs, which fulfill the functions of roots, stalks, and seeds. It needs a good microscope to see the oïdium well, for it is extremely small, as will be seen by the following figures, which express its dimensions. The filaments of the mycelium are from 3 to 5 thousandths of a millimètre (a millimètre is .03937 of an inch) in thickness. Singly they are imperceptible to the naked eye, which can not see them except grouped in masses. The tigelles have a diameter of 4 or 5 thousandths of a millimètre in the narrowest part, at the base ; it is often double that at the top. Their length varies from 7 to 15 hundredths of a millimètre. The spores are of variable sizes; in general their largest diameter is 25 thousandths of a millimètre ; it is often less. Their smallest diameter is about 10 thousandths of a millimètre. The oïdium mould, when it covers all the different parts of a diseased vine, consists, then, of an enormous number of individuals. The fragments of the mycélium reproduce it as scions, and the spores as seeds. Each little surface covered with mould may be considered as a nursery, capable of furnishing a prodigious quantity of reproductive elements, and which the movement of the air will afterward spread abroad on all sides. In hot and damp weather, the oïdium multiplies itself thus very quick by scion as well as seed, and can suddenly infect great extents of vine-plantation. It spreads on the surface of the green parts, and fastens there, interlacing it with a multitude of the filaments of its mycelium, on which sustain themselves, like fibres on a surface of velvet, the tigelles loaded with spores. In the early days of its appearance, the tissues on which it spreads are not impaired; but, little by little, they discolor, rot, and are destroyed. There results from this a disorganization which af fects the parts over which the oïdium spreads, and especially the grapes. We may then prevent the bad effects of this parasite by attacking and destroying it as soon as we see it appear, and before it is well established on all the vines of the vineyard; whereas, if we wait too long, the evil is done, and no remedy can avail. DIFFERENT OPINIONS ON THE VINE DISEASE. This assemblage of properties so peculiar explains why the disease propagates itself and develops; how it effects such ravages when circumstances favor the vegetation of the mushroom, and do not oppose its development. Many observers also consider this cryptogam as the cause of the disease. Their opinion has still greater force, since it has been proved that the disease can be cured, on parts newly attacked, by simply rubbing it off, or by destroying it in any other mode. Thus the direct study of the disease has brought us to these conclusions: 1. That it is by the oïdium alone that we recognize it. 2. That its disappearance, wherever it has not af fected the tissues, is marked by the disappearance of the disease and of its effects. The logical consequence of these conclusions is that the oïdium produces the disease of the vine by developing itself upon it, by disturbing its vegetation, and by exhausting it after the manner of parasites. Other opinions are brought forward; they are of |