Chapter 21

The destructive silk-worm disease, _Botrytis Bassiana_, is also a fungus which attacks and destroys the living insect, concerning which an immense deal has been written, but which has not yet been eradicated. It has also been supposed that a low form or imperfect condition of a mould has much to do with the disease of bees known as "foul brood."[S]

_Penicillium Fieberi_, figured by Corda on a beetle, was doubtless developed entirely after death, with which event it had probably nothing whatever to do.[T] Sufficient, however, has been written to show that fungi have an influence on insect life, and this might be extended to other animal forms, as to spiders, on which one or two species of _Isaria_ are developed, whilst Dr. Leidy has recorded observations on _Julus_[U] which may be perused with advantage. Fish are subject to a mouldy-looking parasite belonging to the _Saprolegniei_, and a similar form attacks the ova of toads and frogs. Gold fish in globes and aquaria are very subject to attack from this mouldy enemy, and although we have seen them recover under a constant change of water, this is by no means always the case, for in a few weeks the parasite will usually prevail.

The influence of fungi upon animals in countries other than European is very little known, except in the case of the species of _Torrubia_ found on insects, and the diseases to which silkworms are subject. Instances have been recorded of the occurrence of fungoid mycelium--for in most it is nothing more--in the tissues of animals, in the hard structure of bone and shell, in the intestines, lungs, and other fleshy parts, and in various organs of birds.[V] In some of the latter cases it has been described as a Mucor, in most it is merely cells without sufficient character for determination. It is by no means improbable that fungi may be found in such situations; the only question with regard to them is whether they are not accidental, and not the producers of unhealthy or diseased tissues, even when found in proximity thereto.

There is one phase of the influences of fungi on the lower animals which must not be wholly passed over, and that is the relation which they bear to some of the insect tribes in furnishing them with food. It is especially the case with the _Coleoptera_ that many species seem to be entirely dependent on fungi for existence, since they are found in no other situations. Beetle-hunters tell us that old _Polyporei_, and similar fungi of a corky or woody nature, are always sought after for certain species which they seek in vain elsewhere,[W] and those who possess herbaria know how destructive certain minute members of the animal kingdom are to their choicest specimens, against whose depredations even poison is sometimes unavailing.

Some of the Uredines, as _Trichobasis suaveolens_ and _Coleosporium sonchi_, are generally accompanied by a little orange larva which preys upon the fungus; and in the United States Dr. Bolles informs us that some species of _Æcidium_ are so constantly infested with this red larva that it is scarcely possible to get a good specimen, or to keep it from its sworn enemy. Minute _Anguillidæ_ revel in tufts of mould, and fleshy Agarics, as they pass into decay, become colonies of insect life. Small _Lepidoptera_, belonging to the _Tineina_, appear to have a liking for such _Polyporei_ as _P. sulfureus_ when it becomes dry and hard, or _P. squamosus_ when it has attained a similar condition. _Acari_ and _Psocidæ_ attack dried fungi of all kinds, and speedily reduce them to an unrecognizable powder.

III. What are the influences exerted by fungi on other plants? This is a broad subject, but withal an important one, since these influences act indirectly on man as well as on the lower animals. On man, inasmuch as it interferes with the vegetable portion of his food, either by checking its production or depreciating its quality. On the lower animals, since by this means not only is their natural food deteriorated or diminished, but through it injurious effects are liable to be produced by the introduction of minute fungi into the system. These remarks apply mainly to fungi which are parasitic on living plants. On the other hand, the influence of fungi must not be lost sight of as the scavengers of nature when dealing with dead and decaying vegetable matter. Therefore, as in other instances, we have here also good and bad influences intermingled, so that it cannot be said that they are wholly evil, or unmixed good.

Wherever we encounter decaying vegetable matter we meet with fungi, living upon and at the expense of decay, appropriating the changed elements of previous vegetable life to the support of a new generation, and hastening disintegration and assimilation with the soil. No one can have observed the mycelium of fungi at work on old stumps, twigs, and decayed wood, without being struck with the rapidity and certainty with which disintegration is being carried on. The gardener casts on one side, in a pile as rubbish, twigs and cuttings from his trees, which are useless to him, but which have all derived much from the soil on which they flourished. Shortly fungi make their appearance in species almost innumerable, sending their subtle threads of mycelium deep into the tissues of the woody substance, and the whole mass teems with new life. In this metamorphosis as the fungi flourish so the twigs decay, for the new life is supported at the expense of the old, and together the destroyers and their victims return as useful constituents to the soil from whence they were derived, and form fresh pabulum for a succeeding season of green leaves and sweet flowers. In woods and forests we can even more readily appreciate the good offices of fungi in accelerating the decay of fallen leaves and twigs which surround the base of the parent trees. In such places Nature is left absolutely to her own resources, and what man would accomplish in his carefully attended gardens and shrubberies must here be done without his aid. What we call decay is merely change; change of form, change of relationship, change of composition; and all these changes are effected by various combined agencies--water, air, light, heat, these furnishing new and suitable conditions for the development of a new race of vegetables. These, by their vigorous growth, continue what water and oxygen, stimulated by light and heat, had begun, and as they flourish for a brief season on the fallen glories of the past summer, make preparation for the coming spring.

Unfortunately this destructive power of fungi over vegetable tissues is too often exemplified in a manner which man does not approve. The dry rot is a name which has been given to the ravages of more than one species of fungus which flourishes at the expense of the timber it destroys. One of these forms of dry rot fungus is _Merulius lacrymans_, which is sometimes spoken of as if it were the only one, though perhaps the most destructive in houses. Another is _Polyporus hybridus_, which attacks oak-built vessels;[X] and these are not the only ones which are capable of mischief. It appears that the dry rot fungus acts indirectly on the wood, whose cells are saturated with its juice, and in consequence lose their lignine and cellulose, though their walls suffer no corrosion. The different forms of decay in wood are accompanied by fungi, which either completely destroy the tissue, or alter its nature so much by the abstraction of the cellulose and lignine, that it becomes loose and friable. Thus fungi induce the rapid destruction of decaying wood. These are the conclusions determined by Schacht, in his memoir on the subject.[Y]

We may allude, in passing, to another phase of destructiveness in the mycelium of fungi, which traverse the soil and interfere most injuriously with the growth of shrubs and trees. The reader of journals devoted to horticulture will not fail to notice the constant appeals for advice to stop the work of fungi in the soil, which sometimes threatens vines, at others conifers, and at others rhododendrons. Dead leaves, and other vegetable substances, not thoroughly and completely decayed, are almost sure to introduce this unwelcome element.

Living plants suffer considerably from the predations of parasitic species, and foremost amongst these in importance are those which attack the cereals. The corn mildew and its accompanying rust are cosmopolitan, as far as we know, wherever corn is cultivated, whether in Australia or on the slopes of the Himalayas. The same may also be said of smut, for _Ustilago_ is as common in Asia and America as in Europe. We have seen it on numerous grasses as well as on barley from the Punjab, and a species different from _Ustilago maydis_ on the male florets of maize from the same locality. In addition to this, we learn that in 1870 one form made its appearance on rice. It was described as constituting in some of the infested grains a whitish, gummy, interlaced, ill-defined, thread-like mycelium, growing at the expense of the tissues of the affected organs, and at last becoming converted into a more or less coherent mass of spores, of a dirty green colour, on the exterior of the deformed grains. Beneath the outer coating the aggregated spores are of a bright orange red; the central portion has a vesicular appearance, and is white in colour.[Z] It is difficult to determine from the description what this so-called _Ustilago_ may be, which was said to have affected a considerable portion of the standing rice crop in the vicinity of Diamond Harbour.

Bunt is another pest (_Tilletia caries_) which occupies the whole farinaceous portion of the grains of wheat. Since dressing the seed wheat has been so widely adopted in this country, this pest has been of comparatively little trouble. Sorghum and the small millets, in countries where these are cultivated for food, are liable to attacks from allied parasites. Ergot attacks wheat and rice as well as rye, but not to such an extent as to have any important influence upon the crop. Two or three other species of fungi are sometimes locally troublesome, as _Dilophospora graminis_, and _Septoria nodorum_ on wheat, but not to any considerable extent. In countries where maize is extensively grown it has not only its own species of mildew (_Puccinia_), but also one of the most enormous and destructive species of _Ustilago_.

A singular parasite on grasses was found by Cesati in Italy, in 1850, infesting the glumes of _Andropogon_.[a] It received the name of _Cerebella Andropogonis_, but it never appears to have increased and spread to such an extent as was at first feared.

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 identity 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. Hassall 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 _Sphærotheca Castagnei_, Lév., 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_, Lév., and _Glæosporium concentricum_, Grev., destructive to cabbages and other cruciferous plants; _Trichobasis Fabæ_, Lév., unsparing when once established on beans; _Erysiphe Martii_, Lév., 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 _Sphæria 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 classed 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 multitudinous. The dried specimens have a sweet scent resembling violets. In Northern Europe _Cæoma 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_, Lév., or poplars and aspens by _Melampsora populina_, Lév., and _Melampsora tremulæ_, Lév., 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 Rosæ_. Still more disastrous is a species of _Erysiphei_, which at first appears like a dense white mould. This is named _Sphærotheca 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 Violæ_. The garden anemone is freely attacked by _Æcidium 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]