of black mildews. Few objects, it may be remarked, are more beautiful under the microscope than the wheelshaped, ray-like processes which radiate from the seedbearing organs. These sporiferous bodies sometimes contain a perfect miniature plant or embryo, similar to that of flowering plants, which waits only circumstances favourable for its expansion. Another allied species, called Fusarium mori, is produced in such abundance on the leaves of the mulberry, in Syria and China, as materially to diminish the supply of food provided for the silk-worm.

But it is not only in food and luxuries that man

suffers from the ravages of fungi; he also suffers in his property. Builders have painful knowledge of one or two species, known under the common name of dry-rot. This most destructive plague is usually caused in this country by the Merulius lachrymans (Fig. 41). It occurs on the inside of wainscoting, in the hollow trunks of trees, in the timber of ships, and in the floors and

beams of buildings in moist, warm situations, where there is not a free circulation of air. It appears at first in round, white, cottony patches, from one to eight inches broad, which afterwards develop over their whole surface a number of fine, yellow, orange, or reddishbrown irregular folds, most frequently so arranged as to. have the appearance of pores, and distilling drops of moisture when perfect; whence its specific name. In the mature state it produces an immense number of minute, rusty sporules, which alight and speedily vegetate in the circumjacent timber, however sound and dry it may appear, destroying its elasticity and toughness, and rendering it incapable of resisting any pressure, until gradually it crumbles into dry, brown dust. This insidious disease, once established, spreads with amazing rapidity, destroying some of the best and most solid-looking houses in a few years. The ships in the Crimea suffered more from this cause than from the ravages of fire, or the shot and shells of the enemy. So virulent is its nature, that it

extends from the woodwork of a house even to the walls themselves, and by penetrating their interstices, crumbles them into pieces. "I knew," says Professor Burnett, "a house into which the rot gained admittance, and which, during the four years we rented it, had the parlours twice wainscoted, and a new flight of stairs, the dry-rot having rendered it unsafe to go from the ground floor to the bed-rooms. Every precaution was taken to remove the decaying timbers when the new work was done; yet the dry-rot so rapidly gained strength that the house was ultimately pulled down. Some of my books which suffered least, and which I still retain, bear

mournful impressions of its ruthless hand; others were so much affected that the leaves resemble tinder, and when the volumes were opened, fell out in dust or fragments." There are no means of restoring to a sound state timber thus decayed; and the dry-rot can only be cured or prevented from spreading by removing the affected parts, clearing away all the fungi, and destroying -by a strong solution of iron, copper, or zinc-the vegetative sporules with which the stones upon which the timbers rest may have been impregnated. Many practical persons have written upon this disease; and the remedies proposed are as numerous as their authors. But the only certain preventives of the evil seem to be the removal of the decaying and contagious matter, the impregnation of the surrounding wood with a strong solution of corrosive sublimate, or the white of an egg, and the admission of a free current of air. Much also may be done by cutting timber, destined for building purposes, in winter, when fungi are usually dormant or dead, and properly seasoning it by steeping it in water for some time, and then thoroughly drying it before it is used. Houses, in order to be free from this plague, should be built in dry, open, and airy situations, and efficiently ventilated throughout every part, especially of the wood-work; when these conditions are observed, this evil will disappear.

In concluding this notice of the destructive fungi, mention may be made of a peculiar form of Penicillium or mould, which is almost invariably present in the solution of copper employed in the process of electrotyping. It proves an intolerable nuisance, inasmuch as it is often

invested with a silver coat, and injures the beauty and the finish of the articles which are subjected to the process. It is extraordinary that the poisonous nature of the solution does not destroy it; but it has been often observed that various species of mould luxuriate in solutions of arsenic, opium, and other poisonous chemical substances, which would prove instantly fatal to all other plants.

It is worthy of remark that the destructive effects of all these parasitic fungi may, in most circumstances, be easily neutralized or prevented by a little intelligent forethought, care, and industry; and providing incentives as they do to the exercise of these qualities, they compensate morally in some measure for the physical evils they occasion. Certain conditions are necessary for their development, and it is to obviating and removing these, that the builder and the farmer must look for exemption from the destructive vegetable diseases that affect their properties. It has been ascertained, for instance, that rust and blight arise from the over-manuring of fields; the grain gorged with too copious a supply of nutritious juices, being brought into a favourable condition for the development of the dormant seeds of fungi which the wind may have wafted to it. The tendency in corn to form these diseases therefore may be destroyed by steeping the seed before sowing in a corrosive solution or in brine; but the same end may be secured in a dry season, and on a favourable soil, by moderate manuring, or by a free use of saline manures.

With regard to the mildew in wheat, it has been suggested by Mr. Tycho Wing, as a remedy, to allow no

reeds or loose grass to remain in the ditches, but to clear everything away, and to consume it at once. "As the species which attacks reeds and grass is to all appearance the same with that of the wheat, the disease may be propagated in the spring from such outliers. For the same reason, it is desirable that the stubble should not be left on the land too long, and, indeed, long mowing must be better than reaping." The various mildews that appear on the grape and other fruits and useful plants, may easily be prevented from developing themselves by the application, at an early stage, of powdered sulphur, which, combining as it does with the oxygen of the atmosphere, forms sulphuric acid, the only chemical poison destructive to moulds and mildews.

Fungi, owing to their cellular and perishable nature, do not usually occur in a fossil state. Some slight traces of them, however, now and then occur among the relics of a former state of things. Species of mould have occasionally been found in the amber beds of the tertiary formation—having been deposited and developed on the resinous juices of the amber pines, just as filaments of mould are often seen at the present day adhering to the gum of apricot and cherry trees. These tiny plants, identical as they are with the common green and blue moulds that infest our cupboards, leave us no room to doubt that fungi were as prevalent and destructive in former epochs as they are now. M. Goeppert, who has examined minutely the amber of various lands, has detected in it, besides moulds, fragments of mosses, hepaticæ, and lichens, perfectly preserved, as in a mummy case, the sole insignificant relics of that vast