are expanding. They are not produced on the higher parts of Fungi are also produced from the granules of the

trees.

mycelium.

The above considerations, which have not appeared, as we believe, in any English work, dispose of the question as regards the more highly organised fungi. At the same time it is to be observed that Fries is an advocate of equivocal generation in Entozòa, Infusòria, Entophyta, and Phylleriàcea, whose life and organisation are derived (as it is said) only from the matrix. He does not allow it as regards the more perfect fungi, there not being any instance of such a thing taking place, any more than in the Usterophyta, among perfect plants.

Let us now turn to what M. Unger says of the Entophyta, in proof of their being mere pustules.

He shows, both by indirect and direct proof, that they originate almost constantly at or near the stomata, the organs, it is to be observed, through which the aqueous and gaseous exhalations take place. M. Bauer observed the same fact in the mildew of wheat, an account of which is given in the Annals of Botany for 1806.

The following are considered by M. Unger as predisposing

1. It is to be remarked that it is always on plants which are young and full of sap that they originate; and hence it is in spring that they are found on the young and tender parts of vegetables.

2. In trees, the young shoots are most subject to be attacked. The Urédines of willows scarely ever originate on leaves fully developed. Urèdo ovata Vaccínii is found only on the new shoots.

3. Younger trees are more predisposed than older. Many species in consequence occur in young plantations, which it is difficult to meet with in those of older growth.

4. Galls are frequently covered with Urédines.

5. The lower branches are more affected than the upper, and the propagation takes place from the base towards the summit. 6. Land too much manured or too rank predisposes corn to

rust.

From all which he concludes that an energetic vitality, but ill-balanced in its different functions, is one of the principal causes of the appearance of entophytes.

As occasional causes the following are noted:

1. An atmosphere habitually charged with water.

2. Absence of light.

3. Sudden changes in the constitution of the atmosphere, as a transition from heat to cold, or from a dry to a moist season. 4. Long-continued drought.

5. Crowded growth.

6. Plants with creeping stems are most subject to attack, as Glechòma, Ficària, &c.

7. Leaves soiled with earth or other impurities are attacked, when those in the neighbourhood which are clean are free.

8. Change of climate, causing corresponding changes in the developement of the plant. Foreign wheat, for instance, sown in Switzerland, is not affected by bunt for the two or three first generations.

9. Inundations. After the inundation of the Danube, at the close of the winter of 1830, all the plants which the year before were healthy were covered with mildew.

Under the influence of such causes the intercellular passages are enlarged by an unusual flow of sap, and from thence the juice is poured into the cavity of the stomata. There it thickens and is coagulated. By reaction on the walls which surround it, the matter thus congested acquires a sort of membranous integument, after which it goes through different degrees of developement, and, under various circumstances, species of different entophytous genera are at length perfected.

At first soft and colourless, and scarcely distinct from the juice which fills the other intercellular passages, it is presently coloured towards the margin. The tint decreases from the circumference to the centre. In some cases, when the cells are loosely connected, the pustule is developed in some part not immediately beneath the stomata: while the malady is confined to the intercellular passages, the neighbouring parts do not partake of the morbid condition; soon, however, the cellular tissue is affected. Each utricle being a distinct organ, with its own circulation, secretion, and excretion, it is impossible for it not to suffer when it is surrounded on every side by stagnating juices. Deranged in its expiratory functions, the cell is filled with unelaborated juice, in which the chlorophyll is no longer formed, so that all parts which surround the growing pustule are blanched, and the neighbouring intercellular passages enlarged.

It would carry us to too great length, neither is it necessary for our purpose, to go into the different appearances presented when each genus is developed. As a general sketch the above is quite sufficient; but after all, without calling in question any part of the author's statements and reasonings, the facts and arguments amount only to this, that entophytous fungi are produced generally within the stomata whose cavities are gorged with sap in a more or less diseased state, which affords at once a nidus and nutriment for the parasite. But this is no proof at all that the entophyte is merely a developement of such sap. Why should it not be just as well inferred, for it is in accordance with other arguments and facts which have been often

stated, that the reproductive granules being present in the plant excite it preternaturally, and cause this unusual flow, and at length stagnation, of the sap, profiting by it when accumulated. And since careful experiments and the constant experience of agriculturists show that they are certainly propagated by sporidia, and that these are absorbed by the radicles, and are carried to various parts of the plant with the sap (a fact sufficient of itself to prove that the productions in question are fungi, though not according to the advocates of equivocal generation, who maintain that a plant or animal once produced may still be able to propagate itself, sufficient proof that they are never equivocally generated), it is clear that in numerous cases some such process must take place; and there is nothing in M. Unger's observations to show that in such case there is any difference in the manner of developement; and, if not, how is it possible to assert that they are ever equivocally generated, except difficulties which do not admit otherwise of easy explanation are at once pronounced, by reason of our ignorance, as proofs of impossibility, a mode of reasoning too frequently adopted. Indeed, M. Unger seems to have felt the difficulty which arises from the affinity of certain moulds which are developed upon various bodies, whose nature cannot be denied, to others which proceed from the stomata of leaves gorged with sap, exactly as is the case with entophytes. The moulds, he says, are formed by a plastic substance, which is elongated into filaments whose extremities separate under the form of spores. They are the result of putrefaction of the juices; the Exanthémata are the product of a sort of fermentation. It is to be observed, however, that such moulds are produced on leaves as free from putrefaction as those on which Entophyta grow; as, for instance, on the common field poppy, Papaver Rhoe'as. However satis factory such a statement may appear to the advocates of equivocal generation, it will, I think, be at once pronounced by any impartial judge a mere string of words without any definite meaning.

Having, then, considered the nature of these entophy tous bodies, it remains that we look to the effect produced by them upon It has been stated above that this, probably, is sometimes beneficial. In a few cases only do they appear to occur in such profusion as to produce the same baneful consequences as the different diseases of the Cereàlia. Whether they be fungi or not (a point now set at rest by the discoveries of Leveillé and Corda), it is clear that if the tree is infested to any great extent, it must suffer by the impediment caused thereby to the free inspiration and expiration, whether gaseous or aqueous, and the withdrawal of abundant nutritive matter, at the expense of which the parasites flourish. In some instances a premature

fall of the leaf is caused, which is seldom unattended by injury. The only remedy in such cases, where the effect is so serious as to fix attention, is to let in as much air as possible by thinning the trees and free pruning. In general, however, the injury to trees appears to be much slighter than that produced on smaller plants. This, indeed, might be inferred from the attention of practical men not having been directed to the point, except perhaps in a single instance. There is, however, a small group of fungi most intimately connected with the Entophyta, and, in fact, forming a member of them, being highly developed Puccinic with the addition of copious gelatine, which is certainly injurious. They originate upon the young shoots and even leaves, and, as they return year after year upon the same base, when the green shoot has become woody, their real nature is scarcely suspected, especially as they have the external form and appearance of Tremélla. The fungi in question, belonging to the genera Podisòma and Gymnosporangium occur in different species of juniper, and materially, though slowly, injure the trees on which they grow.

Besides these especially entophytous fungi there are various species which, though they do not belong to the same group, still are either essentially entophytous, or live upon the surface of leaves, sucking up the juices, which are properly elaborated, except so far as such elaboration may suffer by the constant exhaustion of the sap, and clogging up of the external orifice of many of the stomata. To the first class belong some species of the genera Rhytísma, Dothídea, and Asteròma, &c.; to the latter, of Erysiphe, Perisporium, Oídium, Cladosporium, Septòria, &c. To herbaceous plants some of the species are very injurious, as the Erysiphe of the pea and hop; and many trees suffer more or less from their ravages. Maples especially are frequently seen as it were whitewashed with Erysiphe bicórnis, and evidently suffer, as also does the dogwood from Erysiphe tórtilis. The various varieties of rose are also liable to the attack of Erysiphe pannòsa and Oídium leucocònium, which latter we are much inclined to regard as the infant plant, though the matter has not yet been proved. This is the disease well known to the French nurserymen under the name of Blanc du Rosier. The peach mildew, which is also an Oídium, is too well known as a troublesome inhabitant of peach trees. The common remedy of applying sulphur probably owes its beneficial effects to the force which is used in rubbing it on, which destroys the delicate articulated threads. Amongst the epiphyllous fungi which are injurious to living trees may also be reckoned Cladosporium fumàgo, which appears to be a state of the common Cladosporium herbàrum (E. Pl. f. 16558.) growing upon honey dew. It is the best of many plants in conservatories, especially of orange trees.

It is too frequent in the Isle of Madeira, materially destroying the beauty of the plant, and probably producing much injury. There is still a class of productions arranged by many authors amongst fungi, viz. Eríneum and its allied forms. These, however, are clearly nothing more than anamorphoses of the pubescence arising from unknown causes. In some instances forms of pubescence scarcely differing from some of the lower, socalled, species are normal. Indeed, a strong proof that such is the case exists in the fact that they do not enter well into a systematic arrangement, whereas, without the Entophyta, there would be an irreparable breach in the circle of affinities.

II. We have now to consider shortly those species which attack the wood. These are those which are most noxious, for though they at first grow upon a part already partially decayed, they soon destroy the healthy wood in connexion with the decayed portion, and, if the disease is not stopped by accident, the whole tree soon perishes. It is in general established many years before it shows itself. The rain finds access through some crack or fork, and stagnating decays the portion of wood near it, which becomes a nidus for the developement of some fungus, which remains perhaps for years in the state of mycelium", spreading on every side, and surely, though slowly, working destruction. The fine threads themselves attracting fresh moisture by their own hygrometric nature, soften and decompose the wood, and at length attaining the surface produce a perfect fungus. This appears year after year, acquiring frequently an enormous size, and the tree, when felled, is found to be all but worthless. Sometimes indeed, if the root is not affected all round, a natural cure takes place by the loss of a portion of the trunk or main branch, the decayed part being thus exposed, and the admission of free air preventing the further growth of the fungus. The tree may then last for many years as an object of ornament, but, if the injury is general, a total decay necessarily soon takes place. Where it is desirable to preserve an ornamental tree which is suffering from the attack of fungi, there can be no doubt that a judicious application of corrosive sublimate would effectually prevent the growth of the parasite, but care must be taken that it be not applied in such quantities as to destroy the tree itself.

* Those who wish for a minute analysis of wood infested with the mycelia of fungi, will find the matter treated at length in a work entitled, “ Abhandlung ueber die Verwandlung der polycotyledonischen Pflanzencelle in Pilz und Schwamm Gebilde, und der daraus hervorgehenden sogenannten Fäulniss des Holzes. Dr. Th. Hartig, 1833." In accordance with German views on equivocal generation, he considers the mycelium as a real anamorphosis of the cells of the plant. The details are not adapted to the present publication, and, if such were the case, we have no means of access at present either to the work itself or the review of it in the Linnæa,