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ever they touch. They destroy a plant by covering the surface of its leaves, and thus preventing respiration. Plants are generally most affected by superficial fungi after a long drought, when the fibres of their roots are unable to imbibe sufficient moisture from the soil, and the plant thus becomes debilitated, and affords an easy prey to the parasite which attacks it as a proof, Dr. Lindley mentioned that in Scotland, where there are heavy night dews, this fungus is unknown. The cure seems to be abundant watering. Dr. Lindley mentioned a case of some onions, in the gardens of the Society at Chiswick, which were attacked by this fungus. These onions had been transplanted, and their roots were consequently so much weakened as to be unable to imbibe a sufficient quantity of moisture. Dr. Lindley had the plants abundantly watered, which, though it did not cure the infected plants, appeared completely to arrest the progress of the disease. Other onions, not transplanted, were not attacked. A correspondent of this Magazine (Mr. Haycroft, Vol. VIII. p. 40.) recommends a mode of curing this mildew, which appears to be effectual, by cutting off the infected branches, washing the walls with a composition, and removing the infected nails, &c. Sulphur has also been recommended, but is not found to answer. [For other notices, in this Magazine, on the mildew, see Vol. III. p. 119., Vol. IV. p. 281. 320., Vol. V. p. 107., Vol. VII. p. 87.]

The internal mildew evidently cannot be communicated by the air, since it always appears to spring from the interior of the plant, and to be at first covered with a thin skin, from which it does not burst till it is ripe. It is impossible, therefore, that this kind of mildew can be communicated externally, and yet the fact that it is contagious is so clear as not to admit a doubt. The only manner in which it appears probable that it can reach the interior is through the roots. The seeds, when ripe, fall upon the earth, which becomes contaminated by them, and they are sucked up by the spongioles of the roots. [Mr. Dovaston has, also, held this opinion see Vol. VIII. p. 739.] The correctness of this hypothesis is proved by sowing clean seeds in infected soil; and the young plants from these seeds springing up with the disease upon them. The circumstance of its always attacking the most vigorous plants is thus also explained, as it is evident that, the more rapid the circulation, the greater is the probability of extraneous substances being drawn up with the moisture imbibed by the roots. It is also clear that, in this case, water must aggravate the disease; as, by exciting the plant to suck it up, it would increase the danger of the seeds of the fungi being drawn in with it. This was also the

reason that Mr. Errington found that burying his celery roots only made the mildew spread more rapidly. The only cure for this fungus seems to be that adopted by Mr. Knight with his pear trees, viz., taking them up, washing the roots quite clean from every particle of soil, and then replanting them in quite a different part of his grounds.

Red plants are said to be more liable to mildew than any other. Red is, indeed, supposed by some, always to indicate a morbid action, as it shows that the plant is unable to absorb carbonic acid gas from the atmosphere, which is necessary to its perfect health; at all events, it is a proof of disease when leaves, or any other parts of a plant, not naturally red, assume that colour. Other experiments have been made for curing, or at least preventing the spread of, the internal mildew; and Mr. Bauer has found that steeping grains of corn in limewater will produce the desired effect. There appears no cure for mildew in the roots, but by cutting a deep trench round the infected plants, and cutting off all communication between them and the rest of the field. I regret to have been unable to submit these notes to Professor Lindley: but, if they should contain any thing very erroneous, I will correct it in my introduction to his succeeding lecture on climate. J. W. L.

THE young gardener will find it worth his while to follow up these remarks by a perusal of the enumeration of the genera and species of British funguses in the Hortus Britannicus, and Encyclopedia of Plants, where, besides their names, some information is supplied on their habits. In relation to the above remarks, it is a question, the answer to which would interest, Are all the individual plants of any one species of any genus, to which species a certain species of fungus is peculiar, soil equally eligible, whatever be their condition of health, for the seeds of that fungus to germinate in or upon, and for the plants arising from these seeds to thrive in or upon, and be nourished by? This question is asked in consonance with a view entertained by a thinking friend of ours, who opines that disease, previously to the arrival of the seeds of the fungus, must predispose and prepare the leaves, or other parts, of a plant, as eligible soil for them to germinate in; and that, consequently, parasitic fungi are never the forerunners, but ever the followers, of disease; and, therefore, that, although the seeds of parasitic fungi are, doubtless, dispersed indiscriminately, and fall on the surfaces of vegetables indiscriminately too, they only germinate in and upon those which disease had previously rendered a fit soil for them. — J. D.

ART. XIX. Additional Facts on the Fungus (Æcídium cancellàtum Sowerby) parasitic on the Leaves and Fruit of the Pear Trees in the Garden at Buscot Park. By Mr. JOHN MERRICK.

Sir,

RELATIVELY to the fungus which has been so injurious to my pear trees, and so very grievous to my master,

Pryse Pryse, Esq. M. P., as well as to myself (for no one can see all those beautiful pear trees so much injured by so dreadful a disease without deep regret), I beg to say, that, when I first came to my situation, about nine years since, I found the complaint upon three trees only, and those were upon a north cross wall. I was in hopes that it would soon disappear altogether; but, after a year or two had elapsed, to my great surprise and mortification, I perceived that it got much worse, and that the dreadful disease was spread in different directions in the garden, and had taken its circuit both east and west. It still, year after year, continues its ravages. I certainly can say that I have a few trees that have escaped it in another part of the garden. The trees are for the most part aged, exclusive of those that I have planted since I have been here, which have shared the same fate. All the other trees, I have no doubt, were planted when the garden was first made, which was done by my master's father, E. Loveden, Esq. M.P., about fifty years since. That gentleman was a very great horticulturist, and the garden was made upon a very extensive scale, as he spared no expense. There is nearly a mile of walling, which is from 12 to 14 ft. in height; the soil is a strong stiff loam. There are about 70 fine large pear trees, many of them much admired for their fine spreading branches, each tree covering many yards of the wall. The whole of them throw out their first foliage well at their proper season; but when the leaves are thoroughly expanded, then the disease makes its first appearance by defacing the green leaves with very small red spots. I am, Sir, yours, &c.

Buscot Park, near Farringdon.

Dec. 31. 1832.

JOHN MERRick.

ADDITIONAL to the remarks on this subject made in Vol. VIII. p. 738, 739. we have now nought to present, except the following quotation from Sowerby's English Fungi, wherein, t. 409. and 410., two coloured figures of the fungus are given, which we have copied and given in p. 329., and detailed descriptions of its forms and habits. On these enough has been said; and we confine our quotation to Mr. Sowerby's hints for preventing its increase. "Ecídium cancellàtum has been long a troublesome parasite in many places, and has been the cause of much loss as to the trees which it attacks, as well as in expensive and useless attempts to get rid of it. I think, however, its very nature, like the dry rot, bespeaks an easy cure; but easy cures do not always

gain the confidence due to them. I did not dare to give an easy receipt for the cure of the dry rot, till it was proved to be a good one by Lord Heathfield, who found it succeed. I now may, therefore, venture to give my opinion. By my advice, Lord Heathfield caused proper passages for the admission of common dry air, which became an effectual cure; and I persist in it, that, where there is a certain proportion of dry air, these fungi are not to be found, but only in those seasons when such is natural to the climate. They indicate a certain temperature, like a thermometer, pointing it out when we otherwise do not perceive it; and we may be assured that a certain degree of moisture and temperature is as necessary for the growth of the fungus tribe as any other." These remarks, although they do not supply a definite prescription, may not be wholly useless. Mr. Sowerby was furnished with specimens on June 17. 1807, by John Walker, Esq., of "some wall trees, at his seat at Southgate; it covered, nearly in this manner, a large number of trees. Mr. Walker had the leaves stripped from the trees.

On October 12. 1807, William Lewis, Esq., sent me, from Hendon, the leaves of a Chaumontelle pear tree, which grew against an open fence, the inclination of which was to the south-east."

Mr. Merrick will find farther notices on this subject, in p. 329. 332. of the present Number: Mr. Knight's mode of preventing the effects of the Ecídium cancellatum will be impracticable in the case of trees so old and large as those under the care of Mr. Merrick.

In further connection with the preceding mention of blights by fungus, we shall here introduce to the consideration and canvassing of our practical friends some notices on blights produced on plants by insects: they are written by Rusticus of Godalming, a valued contributor to our Magazine of Natural History; but are published in the Entomological Magazine, an excellent quarterly journal, price 3s. 6d. a number, devoted solely to information on insects. We feel no apprehension of the proprietors of that work being at all displeased at the liberty we are taking, as we know their foremost wish is to diffuse entomological knowledge.

"Observations on the Blights of the Apple" Tree, and its Fruit." I don't know why our brethren on the other side the Atlantic are charged with sending us the greatest pest of our orchards; but so it is. We call an insect the American blight, which, for aught I could ever make out, may have come from China or Botany Bay. However, a name once in vogue will have its day; and one might as well attempt to turn a pig in an entry as argue against an established belief; so American

blight it shall be. In very hot weather you may now and then see this blight on the wing; it has just the look of a bit of cotton, or a downy seed, floating in the air, and is driven by every breath of wind quite as readily. If you catch and examine it, you will find it to be just like the plant-louse which infests our rose trees, &c.: but, unlike all other plant-lice, it is clothed and muffled up with cotton wool, in such quantities, that you would at first have no more idea that the lump contained an insect, than that the mass of clothes on a stage-coach box, in winter, contained a man. Some folks wonder what can be the use of so much clothing; I am not much of a theorist, but I should guess that the vermin came from the torrid zone, and Nature kindly furnishes this garment to protect them from the cold of our climate.

"These blights wander wherever it pleases the wind to carry them; and, if bad luck should drive one of them against the branch of an apple tree, there it will stick, creep into a crack in the bark, bring forth its young, and found a colony: the white cotton soon appears in large bunches; branch after branch becomes infected; the tree grows cankery, pines, and dies. How this is effected no one knows, though the cause and effect are too evident to escape the notice of the commonest clown. In large orchards it is vain to hope for a cure, but not so in gardens. Directly you see the least morsel of cotton, make up your mind to a little trouble, and you will get rid of it. In the first place, get a plasterer's whitewashingbrush, then get a large pot of double size, make your man heat it till it is quite liquid, then go with him into the garden and see that he paints over every patch of white, though not bigger than a sixpence; the next morning have the size-pot heated again, and have another hunt; and keep on doing so every morning for a fortnight. Your man will tell you it's no use; tell him that's your business, not his: your neighbours will laugh at you for your pains; do it before they are up. I have tried it, and know it to be effectual. Spirit of tar has been used with partial effect, so also has resin; whitewashing has been often tried, and, as it contains some size, is not entirely useless, and some horticulturists think it ornamental: I do not."

We now present from correspondents the following remarks on

The American Bug, or Cotton Insect (Aphis lanígera), which is of great consequence when speaking of the diseases of apple trees. It appears to be spreading continually into new districts, though its method of travelling is uncertain. I have known it make its appearance in gardens far removed from

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