Even more destructive than any of these is the potato disease[b]

(_Peronospora infestans_), which is, unfortunately, too well known to need description. This disease was at one time attributed to various causes, but long since its ascertained source has been acknowledged to be a species of white mould, which also attacks tomatoes, but less vigorously. De Bary has given considerable attention to this disease, and his opinions are clearly detailed in his memoir on _Peronospora_, as well as in his special pamphlet on the potato disease.[c] One sees the cause of the epidemic, he says, in the diseased state of the potato itself, produced either accidentally by unfavourable conditions of soil and atmosphere, or by a depravation that the plant has experienced in its culture. According to these opinions, the vegetation of the parasite would be purely accidental, the disease would be independent of it, the parasite would be able frequently even to spare the diseased organs. Others see in the vegetation of the _Peronospora_ the immediate or indirect cause of the various symptoms of the disease; either that the parasite invades the stalks of the potato, and in destroying them, or, so to speak, in poisoning them, determines a diseased state of the tubercles, or that it introduces itself into all the organs of the plant, and that its vegetation is the immediate cause of all the symptoms of the disease that one meets with in any organ whatever. His observations rigorously proved that the opinions of the latter were those only which were well founded.

All the alterations seen on examining spontaneous individuals are found when the _Peronospora_ is sown in a nourishing plant. The most scrupulous examination demonstrates the most perfect ident.i.ty between the cultivated and spontaneous individuals as much in the organization of the parasite as in the alteration of the plant that nourishes it.

In the experiments that he had made he affirms that he never observed an individual or unhealthy predisposition of the nourishing plant. It appeared to him, on the contrary, that the more the plant was healthy, the more the mould prospered.

We cannot follow him through all the details of the growth and development of the disease, or of his experiments on this and allied species, which resulted in the affirmation that the mould immediately determines the disease of the tubercles as well as that of the leaves, and that the vegetation of the _Peronospora_ alone determines the redoubtable epidemic to which the potato is exposed.[d] We believe that this same observer is still engaged in a series of observations, with the view, if possible, of suggesting some remedy or mitigation of the disease.

Dr. Ha.s.sall pointed out, many years since, the action of fungous mycelium, when coming in contact with cellular tissue, of inducing decomposition, a fact which has been fully confirmed by Berkeley.

Unfortunately there are other species of the same genus of moulds which are very destructive to garden produce. _Peronospora gangliformis_, B., attacks lettuces, and is but too common and injurious. _Peronospora effusa_, Grev., is found on spinach and allied plants. _Peronospora Schleideniana_, D. By., is in some years very common and destructive to young onions, and field crops of lucerne are very liable to attack from _Peronospora trifoliorum_, D. By.

The vine crops are liable to be seriously affected by a species of mould, which is but the conidia form of a species of _Erysiphe_. This mould, known under the name of _Oidium Tuckeri_, B., attacks the vines in hothouses in this country, but on the Continent the vineyards often suffer severely[e] from its depredations; unfortunately, not the only pest to which the vine is subject, for an insect threatens to be even more destructive.

Hop gardens suffer severely, in some years, from a similar disease; in this instance the mature or ultimate form is perfected. The hop mildew is _Sphaerotheca Castagnei_, Lev., which first appears as whitish mouldy blotches on the leaves, soon becoming discoloured, and developing the black receptacles on either surface of the leaf. These may be regarded as the cardinal diseases of fungoid origin to which useful plants are subject in this country.

Amongst those of less importance, but still troublesome enough to secure the anathemas of cultivators, may be mentioned _Puccinia Apii_, Ca., often successful in spoiling beds of celery by attacking the leaves; _Cystopus candidus_, Lev., and _Glaeosporium concentric.u.m_, Grev., destructive to cabbages and other cruciferous plants; _Trichobasis Fabae_, Lev., unsparing when once established on beans; _Erysiphe Martii_, Lev., in some seasons a great nuisance to the crop of peas.

Fruit trees do not wholly escape, for _Roestelia cancellata_, Tul., attacks the leaves of the pear. _Puccinia prunorum_ affects the leaves of almost all the varieties of plum. Blisters caused by _Ascomyces deformans_, B., contort the leaves of peaches, as _Ascomyces bullatus_, B., does those of the pear, and _Ascomyces juglandis_, B., those of the walnut. Happily we do not at present suffer from _Ascomyces pruni_, Fchl., which, on the Continent, attacks young plum-fruits, causing them to shrivel and fall. During the past year pear-blossoms have suffered from what seems to be a form of _Helminthosporium pyrorum_, and the branches are sometimes infected with _Capnodium elongatum_; but orchards in the United States have a worse foe in the "black knot,"[f] which causes gouty swellings in the branches, and is caused by the _Sphaeria morbosa_ of Schweinitz.

Cotton plants in India[g] were described by Dr. Shortt as subject to the attacks of a kind of mildew, which from the description appeared to be a species of _Erysiphe_, but on receiving specimens from India for examination, we found it to be one of those diseased conditions of tissue formerly cla.s.sed with fungi under the name of _Erineum_; and a species of Torula attacks cotton pods after they are ripe. Tea leaves in plantations in Cachar have been said to suffer from some sort of blight, but in all that we have seen insects appear to be the depredators, although on the decaying leaves _Hendersonia theicola_, Cooke, establishes itself.[h] The coffee plantations of Ceylon suffer from the depredations of _Hemiliea vastatrix_, as well as from insects.[i] Other useful plants have also their enemies in parasitic fungi.

Olive-trees in the south of Europe suffer from the attacks of a species of _Antennaria_, as do also orange and lemon trees from a _Capnodium_, which covers the foliage as if with a coating of soot. In fact most useful plants appear to have some enemy to contend with, and it is fortunate, not only for the plant, but its cultivators, if this enemy is less exacting than is the case with the potato, the vine, and the hop.

Forestry in Britain is an insignificant interest compared to what it is in some parts of Europe, in the United States, and in our Indian possessions. In these latter places it becomes a matter of importance to inquire what influence fungi exert on forest trees.

It may, however, be predicated that the injury caused by fungi is far outstripped by insects, and that there are not many fungi which become pests in such situations. Coniferous trees may be infested with the species of _Peridermium_, which are undoubtedly injurious, _Peridermium elatinum_, Lk., distorting and disfiguring the silver fir, as _Peridermium Thomsoni_, B.,[j] does those of _Abies Smithiana_ in the Himalayas. This species occurred at an elevation of 8,000 feet. The leaves become reduced in length one-half, curved, and sprinkled, sometimes in double rows, with the large sori of this species, which gives the tree a strange appearance, and at length proves fatal, from the immense diversion of nutriment requisite to support a parasite so large and mult.i.tudinous. The dried specimens have a sweet scent resembling violets. In Northern Europe _Caeoma pinitorquum_, D. By., seems to be plentiful and destructive. All species of juniper, both in Europe and the United States, are liable to be attacked and distorted by species of _Podisoma_[k] and _Gymnosporangium_. _Antennaria pinophila_, Fr., is undoubtedly injurious, as also are other species of _Antennaria_, which probably attain their more complete development in _Capnodium_, of which _Capnodium Citri_ is troublesome to orange-trees in the south of Europe, and other species to other trees. How far birch-trees are injured by _Dothidea betulina_, Fr., or _Melampsora betulina_, Lev., or poplars and aspens by _Melampsora populina_, Lev., and _Melampsora tremulae_, Lev., we cannot say. The species of _Lecythea_ found on willow leaves have decidedly a prejudicial effect on the growth of the affected plant.

Floriculture has to contend with many fungoid enemies, which sometimes commit great ravages amongst the choicest flowers. Roses have to contend against the two forms of _Phragmidium mucronatum_ as well as _Asteroma Rosae_. Still more disastrous is a species of _Erysiphei_, which at first appears like a dense white mould. This is named _Sphaerotheca pannosa_. Nor is this all, for _Peronospora sparsa_, when it attacks roses in conservatories, is merciless in its exactions.[l]

Sometimes violets will be distorted and spoiled by _Urocystis Violae_.

The garden anemone is freely attacked by _aecidium quadrifidum_.

Orchids are liable to spot from fungi on the leaves, and recently the whole of the choicest hollyhocks have been threatened with destruction by a merciless foe in _Puccinia malvacearum_. This fungus was first made known to the world as an inhabitant of South America many years ago. It seems next to have come into notoriety in the Australian colonies. Then two or three years ago we hear of it for the first time on the continent of Europe, and last year for the first time in any threatening form in our own islands. During the present year its ravages are spreading, until all admirers of hollyhocks begin to feel alarm lest it should entirely exterminate the hollyhock from cultivation. It is common on wild mallows, and cotton cultivators must be on the alert, for there is a probability that other malvaceous plants may suffer.

A writer in the "Gardener's Chronicle" has proposed a remedy for the hollyhock disease, which he hopes will prove effectual. He says, "This terrible disease has now, for twelve months, threatened the complete annihilation of the glorious family of hollyhock, and to baffle all the antidotes that the ingenuity of man could suggest, so rapidly does it spread and accomplish its deadly work. Of this I have had very sad evidence, as last year at this time I had charge of, if not the largest, one of the largest and finest collections of hollyhocks anywhere in cultivation, which had been under my special care for eleven years, and up to within a month of my resigning that position I had observed nothing uncommon amongst them; but before taking my final leave of them I had to witness the melancholy spectacle of bed after bed being smitten down, and amongst them many splendid seedlings, which had cost me years of patience and anxiety to produce. And again, upon taking a share and the management of this business, another infected collection fell to my lot, so that I have been doing earnest battle with this disease since its first appearance amongst us, and I must confess that, up to a very short time back, I had come in for a great deal the worst of the fight, although I had made use of every agent I could imagine as being likely to aid me, and all that many competent friends could suggest. But lately I was reminded of Condy's patent fluid, diluted with water, and at once procured a bottle of the green quality, and applied it in the proportion of a large tablespoonful to one quart of water, and upon examining the plants dressed, twelve hours afterwards, was delighted to find it had effectually destroyed the disease (which is easily discernible, as when it is living and thriving it is of a light grey colour, but when killed it becomes of a rusty black). Further to test the power at which the plant was capable of bearing the antidote without injury, I used it double the strength. This dose was instant death to the pest, leaving no trace of any injury to the foliage. As to its application, I advocate sponging in all dressings of this description. Syringing is a very ready means, but very wasteful. No doubt sponging consumes more time, but taking into consideration the more effectual manner in which the dressing can be executed alone, it is in the end most economical, especially in regard to this little parasite. I have found it difficult by syringing, as it has great power of resisting and throwing off moisture, and if but a very few are left living, it is astonishing how quickly it redistributes itself. I feel confident, that by the application of this remedy in time another season, I shall keep this collection clean. I believe planting the hollyhock in large crowded beds should be avoided, as I have observed the closer they are growing the more virulently does the disease attack them, whereas isolated rows and plants are but little injured."[m]

The "Gardener's Chronicle" has also sounded a note of warning that a species of Uredine has been very destructive to pelargoniums at the Cape of Good Hope. Hitherto these plants have not suffered much in this country from parasites. Besides these, there are many other less troublesome parasites, such as _Uredo filic.u.m_, on ferns; _Puccinia Lychnidearum_, on leaves of sweet-william; _Uredo Orchidis_, on leaves of orchids, &c.

If we would sum up the influences of fungi in a few words, it could be done somewhat in the following form.

Fungi exert a deleterious influence--

On _Man_,

When eaten inadvertently.

By the destruction of his legitimate food.

In producing or aggravating skin diseases.

On _Animals_,

By deteriorating or diminishing their food supplies.

By establishing themselves as parasites on some species.

On _Plants_,

By hastening the decay of timber.

By establishing themselves as parasites.

By impregnating the soil.

But it is not proved that they produce epidemic diseases in man or animals, or that the dissemination of their mult.i.tudinous spores in the atmosphere has any appreciable influence on the health of the human race. Hence their a.s.sociation with cholera, diarrhoea, measles, scarlatina, and the manifold ills that flesh is heir to, as producing or aggravating causes, must, in the present state of our knowledge and experience, be deemed apocryphal.

[A] A detailed account of the peculiar properties of this fungus and its employment as a narcotic will be found in Cooke's "Seven Sisters of Sleep," p. 337. It is figured in Greville's "Scottish Cryptogamic Flora," plate 54.

[B] Pour chaque 500 grammes de champignons coupes en morceaux d'a.s.sez mediocre grandeur, il faut un litre d'eau acidulee par deux ou trois cuillerees de vinaigre, ou deux cuillerees de sel gris. Dans le cas ou l'on n'aurait que de l'eau a sa disposition, il faut la renouveler une ou deux fois. On laisse les champignons macerer dans le liquids pendant deux heures entieres, puis on les lave a grande eau. Ils sont alors mis dans de l'eau froide qu'on porte a l'ebullition, et apres un quart d'heure ou une demi-heure, on les retire, on les lave, on les essuie, et ou les apprete soit comme un mets special, et ils comportent les memes a.s.saisonnements que les autres, soit comme condiment.--_Morel Traite des Champignons_, p. lix. Paris, 1865.

[C] Smith's "Chart of Poisonous Fungi," fig. 10.

[D] Ibid. fig. 27. It would be well to become acquainted with all these figures.

[E] "Skin Diseases of Parasitic Origin," by Dr. Tilbury Fox. London, 1863.

[F] Robin, "Hist. Nat. des Vegetaux Parasites." Paris, 1853.

Kuchenmeister, "Animal and Vegetable Parasites of the Human Body." London, Sydenham Society, 1857.

[G] Berkeley, in "Intellectual Observer," Nov., 1862. "Mycetoma," II.

Vand.y.k.e Carter, 1874.

[H] Hallier and Zurn, "Zeitschrift fur Parasitenkunde." Jena, 1869-71.

[I] Dr. Lauder Lindsay, "On Microscopical and Clinical Characters of Cholera Evacuations," reprinted from "Edinburgh Medical Journal," February and March, 1856; also "Clinical Notes on Cholera," by W. Lauder Lindsay, M.D., F.L.S., in "a.s.sociation Medical Journal" for April 14, 1854.

[J] "Microscopic Examinations of Air," from the "Ninth Annual Report of the Sanitary Commissioner," Calcutta, 1872.

[K] "Gardener's Chronicle," March 26, 1864.

[L] Gray, G., "Notices of Insects that are Known to Form the Bases of Fungoid Parasites." London, 1858.

[M] Halsey, "Ann. Lyceum," New York, 1824, p. 125.

[N] Tulasne, "Selecta Fung. Carp." vol. iii. p. 17.

[O] "Berlin Entom. Zeitung," 1858, p. 178.

[P] "Smithsonian Contributions to Knowledge," v. p. 53.

[Q] "Wiegmann Archiv." 1835, ii. p. 354; "Ann. Nat. Hist." 1841, 405.

[R] Leidy, "Proc. Acad. Nat. Sci. Phil." 1851, p. 204.

[S] "Gardener's Chronicle," November 21, 1868.

[T] Corda, "Prachtflora," pl. ix.