This disease, which has by some been mistaken for the .fire blight, and by others deemed worthy of so little attention, that few notices of its presence, or hints for its destruction, have appeared in your magazine, is, I am persuaded, productive of more injury to nurserymen and those amateurs who undertake the propagation of their own pear and plum standards, than the genuine fire blight.

I propose, therefore, to state some of my views on the subject, hoping that brother nurserymen, at least, will give the readers of the Horticulturist the benefit of their expertence; as I doubt not all of them have consulted their own interest sufficiently to make some experiments upon the matter.

The disease in question makes its first appearance in the shape of small brown spots or blotches, upon the under side of the lower leaves of the trees affected; from thence spreading rapidly to the neighboring leaves and branches, and gradually destroying the foliage, from the bottom upwards, until finally the plants remain leafless, or nearly so, in midsummer or early autumn. They usually attempt a second growth the same season, but the result is only a feeble, sickly shoot, which also sheds prematurely its leaves, and mournfully waits for another season of similar attempts and like success: its spindling branches and thorny stock, giving but poor encouragement to the cultivator, that his utmost skill with budding or puning knife, will cause a vigorous shoot to appear form its hide-bound stem, or induce his puny seedling to assume an air of health and beauty. Alas! bitter experience satisfies him that hope for leaf-blighted stocks is of that character which "makes the heart sick."

Its attacks are not entirely confined to small seedlings or nursery trees, although it is to these that it is most injurious; nor does it limit its depredations to a single town or state; from Belgium to Iowa, its presence is almost universal in grounds which have for any considerable length of time been devoted to the cultivation of pear and plum trees; sometimes a bearing tree is the object of its attention, in which case, a leafless tree in August, with immature and blackened fruit, is the reward of the waiting cultivator; a sorry remuneration to one who has expended his time and patience in catching "Turks," or pinching his pyramids; in cutting off knots, or watching for the first symptom of the fire blight; but as it is not often that its choice falls upon the orchard or standard tree, I shall confine my present remarks to its ravages in the nursery.

It is a fact well known to most nurserymen, that this disease has been the cause of more failures in the rearing of pear and plum trees, both in the nursery row and the seed bed, than all other causes combined. The stock which is attacked becomes impracticable to the budder before the season arrives for inoculation, or if, perchance, he is able to raise the bark sufficiently for his purpose, the languid state of the plant renders his efforts almost useless; and even when he succeeds in working the refractory subject, those which have been severely attacked make, at first, but an indifferent growth. The injury is not always nor commonly mortal, for stocks which have been attacked, appear after working, to recover their health, and finally to make as good trees as others; but the delay and vexation to the nurseryman is intolerable.

In the seed bed, he first discovers small patches, where the smaller and weaker plants have a brownish appearance, and are shedding their lower leaves, which patches increase in size, until the whole bed looks as if a fire had passed over it. If it is his first acquaintance with the pest, he consults some author on fruit trees, but finds no disease treated of which answers the description, and consoles himself with the idea that it will soon disappear; or, perhaps, he applies those universal remedies, lime and ashes, but with no good result. Some afflicted cultivators have, in their desperation, applied salt to their suffering subjects, until the entire disappearance of foliage convinced them that even salt was unable to save. Perhaps he consoles himself with the idea, that when he has them dibbled out in nursery rows, this trouble will be over. But another season's experience convinces him that whatever ailed his stocks, they have carried their ailment with them, and seem determined to perpetuate the indisposition, by giving it to their neighbors.

My observations lead me to the belief, that whatever be the cause of this difficulty, it is not to bo found in the work of an insect. The most critical examination which I have been able to make, has revealed neither insect nor egg, but only a species of rust, or fungus, which spreads oyer the surface of the leaf, and closes the pores, thus producing death.

I am also convinced that it is exceedingly infectious, and that when once a patch of trees has been affected, there is but little hope to the nurseryman, that he will be entirely free from it on that piece of ground. It is also pretty certain, that stocks which are diseased in the seed bed, will carry the complaint with them to the place where they are planted out; but this last result will not always follow - I have, myself, known one (and but one) instance, in which leaf-blighted seedlings, which were removed far away from other trees, recovered entirely their proper health and beauty.

It is impossible to raise pear or plum seedlings which shall be entirely free from this disease, in an old nursery, by any method of prevention or cure which is known to us; most of the old established nurseries have, therefore, depended in a great measure upon purchasing this species of stock, and as its attacks do not seem permanently to injure good sized plants, they are thus enabled to supply their customers with trees, which, when removed to the fruit yard, or the orchard, give entire satisfaction.

One peculiarity has probably been observed by all who have examined this subject, which is, that budded or worked trees are comparatively free from attack; these often retaining their foliage unspotted, and continuing to grow rapidly, while their natural or seedling neighbors are leafless. Why the leaves of our most esteemed varieties are able to withstand attacks which are fatal to those which we are accustomed to believe are more hardy than they, I am at a loss to determine.

The cause of so great an evil as this, deserves, of course, our best attention; but it is still a profound mystery; it makes its appearance without warning, and has no fore-runners, no busy hum of insect, nor endless throng of aphides, ushers in the work of destruction. It cares not for rain, nor does the mighty wind check its steady progress; sunshine and cloud seem to favor, and darkness to offer no obstacle to its work of desolation; lime and ashes, plaster and guano, are but aggravations; even copperas water, and filthy whale oil soap, are alike agreeable to the mysterious visitor; like the unseen malaria, it is known only by its effects. A friend who has some acquaintance with it, believes the po-tatoe rot has attacked his little pear trees.

The cure has not yet transpired, but there is much hope in prevention; my own observations lead me to recommend the planting of pear and plum seeds, and stocks, at a distance, say at least half a mile from any other nursery; the superior advantages of a virgin soil, combined with freedom from adverse influences, will generally be sufficient to ensure at least one healthy crop. Probably many old nurserymen have observed, that beginners usually have their best success (with these trees) first; after this their progress is like that of others, somewhat variable, and against obstacles, of which leaf blight is the chief.

Shall we not hear from others upon this subject, which, although of little consequence to the orchadist, is eminently worthy the attention of nurserymen. H. E. Hooker.

A very interesting article to all the cultivators of the pear, and one which we hope will elicit the remarks of other correspondents. We examined the spots, caused by this leaf-blight, last summer, under a powerful microscope, and are satisfied that, as Mr. H. sugspots and an occasional crack would appear upon the fruit, the pears would cease to swell, and the whole crop would prove an utter failure. Was not this failure of the crop the immediate effect of the attack of this fungus called the leaf blight, and is not this fungus the partial cause of the so-called decline of some of the old varieties? Further observation will establish the truth of these conjectures if they are correct, and as the attacks of fungi are not past prevention, we hope something may also be discovered to answer this purpose. At any rate, this is an important subject of investigation.. Ed.