A very singular case, illustrative of the effects of the mycelium of Fungi arising from dead wood upon neighboring plants, occurred a few years ago in Northamptonshire, England. A Golden Rose, remarkable for the size of its flowers, and a great favorite from the peculiar circumstances under which it was planted, was the subject of conversation amongst a party of friends, who were admiring its beauty, and alluding to the matter of interest with which it was associated. Though apparently in the most vigorous health, the next day it was withered as if killed by a stroke of lightning. The mystery, however, was soon developed. On examination, the roots were found to be covered with a white web of mycelium, which was evidently of extraneous growth. Other instances have occurred of a similar character in the same garden, and we have in consequence been convinced that the principal reason why trees will seldom succeed where an old one has died, is due to fungi arising from the decayed roots. Evidence of a like kind will be found in Loudon's Arboretum, under the article " Larch." The principle, however, is of far wider extent.

A disease was noticed some years since in several parts of England, but especially at Ely, where it is known under the name of Copper Web, as attacking Asparagus. It is due to some mycelium, known to botanists under the name of Rhizoctonium, but of which the perfect form has not yet been ascertained. In France, it is the pest of lucerne, chiccory, saffron, and of several other objects of cultivation.. We believe that it is always traceable either to dead vegetable bodies in the neighborhood of the roots, or to more recent substances like sawdust, mixed in the manure. It is well known, again, that tender annuals often damp off in a frame without any apparent cause. Where leaf-mould or matter from the base of fagot ricks imperfectly rotted, has been mixed with the soil, mycelium developed on the little fragments attacks the roots and kills them; and we have found the same effect arise from lumps of hard cowdung mixed with compost, which are very apt to produce mycelium.

The fungi of which this mycelium is the infant state, in many cases, could by no possibility be developed upon the plants which it destroys, but it should seem as if there was a peculiar tendency in many fungal threads to produce decomposition upon tender cellular tissue with which it may come in contact, and if one cell only be attacked, the taint may easily be communicated from cell to cell in any direction which may be least capable of resistance. If there is any truth in the notion (which, within certain limits, can scarcely be denied) that particular roots have an especial reference to particular branches, we have a ready solution of the mystery, that one branch should perish while the rest of the tree is healthy. In some capes, injury no doubt arises in a different way from contact with decaying vegetable matter, where no mycelium may be produced, and the effect may be precisely the same. An interesting account of injury arising from snch a cause is given in the Bibliotheque des Chemins de Fer, in Payen's treatise on the maladies of several objects of cultivation. It is a matter of experience that sugar beet is extremely subject to decay when sown on ground which had formerly borne a crop of the same vegetable.

The plant is one which sends down a long taproot into the ground, and when the crop is removed, a large portion of this generally remains behind, though at a considerable depth beneath the surface. When the tap-root of the new plant strikes down to this depth, as it will naturally do if vegetation is vigorous, the tender spongelets are affected by the old putrescent roots, and the decay is soon carried upwards, to the destruction of the crop.

The inferences from the subject are obvious, and show the necessity of increased care in many quarters of the garden, where matters have long been left to take their chance. - M. J. B., in Gardeners' Chronicle.