Fungi: Their Nature and Uses Part 18

[j] Specimens were published under this name in Cooke's "Fungi Britannici Exsiccati," No. 359.

[k] Cooke, "On Polymorphism in Fungi," in "Popular Science Review."

[l] Lewis's "Report on Microscopic Objects found in Cholera Evacuations," Calcutta, 1870.

[m] Tulasne, "Selecta Fungorum Carpologia," ii. p. 261.

[n] Corda, "Prachtflora," plate vii.

X.

INFLUENCES AND EFFECTS.

It is no longer doubted that fungi exercise a large and very important influence in the economy of nature. It may be that in some directions these influences are exaggerated; but it is certain that on the whole their influence is far more important for evil and for good than that of any other of the Cryptogamia. In our endeavour to estimate the character and extent of these influences it will prove advantageous to examine them under three sections. 1. Their influence on man. 2. Their influence on lower animals. 3. Their influence on vegetation. Under these sections the chief facts may be grouped, and some approximate idea obtained of the very great importance of this family of inferior plants, and consequently the advisability of pursuing their study more thoroughly and nationally than has. .h.i.therto been done.

I. In estimating the influence of fungi upon man, we naturally enough seek in the first instance to know what baneful effects they are capable of producing on food. Although in the case of "poisonous fungi," popularly understood, fungi may be the pa.s.sive agents, yet they cannot be ignored in an inquiry of this nature. Writing of the Uses of Fungi, we have already shown that a large number are available for food, and some of these real delicacies; so, on the other hand, it becomes imperative, even with stronger emphasis, to declare that many are poisonous, and some of them virulently so. It is not sufficient to say that they are perfectly harmless until voluntarily introduced into the human system, whilst it is well known that accidents are always possible, and probably would be if every baneful fungus had the word POISON inscribed in capitals on its pileus.

The inquiry is constantly being made as to what plain rules can be given for distinguis.h.i.+ng poisonous from edible fungi, and we can answer only that there are none other than those which apply to flowering plants. How can aconite, henbane, oenanthe, stramonium, and such plants, be distinguished from parsley, sorrel, watercress, or spinach? Manifestly not by any general characters, but by specific differences. And so it is with the fungi. We must learn to discriminate _Agaricus muscarius_ from _Agaricus rubescens_, in the same manner as we would discriminate parsley from _aethusa cynapium_.

Indeed, fungi have an advantage in this respect, since one or two general cautions can be given, when none such are applicable for higher plants. For instance, it may be said truly that all fungi that exhibit a rapid change to blue when bruised or broken should be avoided; that all Agarics are open to suspicion which possess an acrid taste; that fungi found growing on wood should not be eaten unless the species is well known; that no species of edible fungus has a strong, unpleasant odour, and similar cautions, which, after all, are insufficient. The only safe guide lies in mastering, one by one, the specific distinctions, and increasing the number of one's own esculents gradually, by dint of knowledge and experience, even as a child learns to distinguish a filbert from an acorn, or with wider experience will thrust in his mouth a leaf of _Oxalis_ and reject that of the white clover.

One of the most deleterious of fungi that we possess is at the same time one of the most beautiful. This is the _Agaricus muscarius_, or Fly Agaric, which is sometimes used as a fly poison.[A] It has a bright crimson pileus studded with pale whitish (sometimes yellowish) warts, and a stem and gills of ivory whiteness. Many instances have been recorded of poisoning by this fungus, and amongst them some British soldiers abroad, and yet it cannot be doubted that this fungus is eaten in Russia. Two instances have come under our notice of persons with some botanical knowledge, and one a gardener, who had resided in Russia and eaten of this fungus. In one case the Fly Agaric was collected and shown to us, and in the other the figure was indicated, so that we might be under no doubt as to the species. Only one hypothesis can be advanced in explanation. It is known that a large number of fungi are eaten in Russia, and that they enter much into the domestic cookery of the peasantry, but it is also known that they pay considerable attention to the mode of cooking, and add a large amount of salt and vinegar, both of which, with long boiling, must be powerful agents in counteracting the poison (probably somewhat volatile) of such fungi as the Fly Agaric. In this place we may give a recipe published by a French author of a process for rendering poisonous fungi edible. It must be taken on his authority, and not our own, as we have never made the experiment, notwithstanding it seems somewhat feasible:--For each pound of mushrooms, cut into moderately small pieces, take a quart of water acidulated with two or three spoonfuls of vinegar, or two spoonfuls of bay salt. Leave the mushrooms to macerate in the liquid for two hours, then wash them with plenty of water; this done, put them in cold water and make them boil.

After a quarter or half hour's boiling take them off and wash them, then drain, and prepare them either as a special dish, or use them for seasoning in the same manner as other species.[B]

This method is said to have been tried successfully with some of the most dangerous kinds. Of these may be mentioned the emetic mushroom, _Russula emetica_, with a bright red pileus and white gills, which has a clear, waxy, tempting appearance, but which is so virulent that a small portion is sufficient to produce disagreeable consequences. It would be safer to eschew all fungi with a red or crimson pileus than to run the risk of indulging in this. A white species, which, however, is not very common, with a bulbous base enclosed in a volva, called _Agaricus vernus_, should also be avoided. The pink spored species should also be regarded with suspicion. Of the _Boleti_ several turn blue when cut or broken, and these again require to be discarded. This is especially the case with _Boletus luridus_[C] and _Boletus Satanas_,[D] two species which have the under surface or orifice of the pores of a vermilion or blood-red colour.

Not only are species which are known to be poisonous to be avoided, but discretion should be used in eating recognized good species. Fungi undergo chemical changes so rapidly that even the cultivated mushroom may cause inconvenience if kept so long after being gathered as to undergo chemical change. It is not enough that they should be of a good kind, but also fresh. The employment of plenty of salt in their preparation is calculated very much to neutralize any deleterious property. Salt, pepper, and vinegar are much more freely employed abroad in preparing fungi than with us, and with manifest advantage.

It is undoubtedly true that fungi exert an important influence in skin diseases. This seems to be admitted on all hands by medical men,[E] however much they may differ on the question of the extent to which they are the cause or consequence of disease. Facts generally seem to bear out the opinion that a great number of skin diseases are aggravated, and even produced, by fungi. Robin[F] insists that a peculiar soil is necessary, and Dr. Fox says it is usually taught that tuberculous, scrofulous, and dirty people furnish the best nidus. It is scarcely necessary to enumerate all these diseases, with which medical men are familiar, but simply to indicate a few.

There is favus or scall-head, called also "porrigo," which has its primary seat in the hair follicles. Plica polonica, which is endemic in Russia, is almost cosmopolitan. Then there is Tinea tonsurans, Alopecia, Sycosis, &c., and in India a more deeply-seated disease, the Madura Foot, has been traced to the ravages of a fungus described under the name of _Chionyphe Carteri_.[G] It is probable that the application of different names to the very often imperfect forms of fungi which are a.s.sociated with different diseases is not scientifically tenable. Perhaps one or two common moulds, such as _Aspergillus_ or _Penicillium_, lie at the base of the majority, but this is of little importance here, and does not affect the general principle that some skin diseases are due to fungi.

Whilst admitting that there are such diseases, it must be understood that diseases have been attributed to fungi as a primary cause, when the evidence does not warrant such a conclusion. Diphtheria and thrush have been referred to the devastations of fungi, whereas diphtheria certainly may and does occur without any trace of fungi. Fevers may sometimes be accompanied by fungoid bodies in the evacuations, but it is very difficult to determine them. The whole question of epidemic diseases being caused by the presence of fungi seems based on most incomplete evidence. Dr. Salisbury was of opinion that camp measles was produced by _Puccinia graminis_, the pseudospores of which germinated in the damp straw, disseminated the resultant secondary bodies in the air, and caused the disease. This has never been verified. Measles, too, has been attributed freely, as well as scarlatina,[H] to fungal influences, and the endeavours to implicate fungi in being the cause of cholera have been pertinaciously persevered in with no conviction. The presence of certain cysts, said to be those of _Urocystis_, derived from rice, was announced by Dr.

Hallier, but when it was shown that no such fungus was found on rice, this phase of the theory collapsed. Special and competent experts were sent from this country to examine the preparations and hear the explanations of Dr. Hallier on his theory of cholera contagion, but they were neither convinced nor satisfied.

As long ago as 1853, Dr. Lauder Lindsay examined and reported on cholera evacuations, and in 1856 he declared--"It will be evident that I can see no satisfactory groundwork for the fungus theory of cholera, which I am not a little surprised to find still possesses powerful advocates."[I] And of the examinations undertaken by him he writes:--"The mycelium and sporules of various species of fungi, const.i.tuting various forms of vegetable mould, were found in the sc.u.m of the vomit, as well as of the stools, but only at some stage of decomposition. They are found, however, under similar circ.u.mstances, in the vomit and stools of other diseases, and, indeed, in all decomposing animal fluids, and they are therefore far from peculiar to cholera."

Some writers have held that the atmosphere is often highly charged with fungi spores, others have denied the presence of organic bodies to any extent in the air. The experiments conducted in India by Dr.

Cunningham[J] have been convincing enough on this point. This report states that spores and similar cells were of constant occurrence, and were generally present in considerable numbers. That the majority of the cells were living and ready to undergo development on meeting with suitable conditions was very manifest, as in those cases in which preparations were retained under observation for any length of time, germination rapidly took place in many of the cells; indeed, many spores already germinating were deposited on the slides. In few instances did any development take place beyond the formation of mycelium or ma.s.ses of toruloid cells, but in one or two distinct sporules were developed on the filaments arising from some of the larger septate spores, and in a few others _Penicillium_ and _Aspergillus_ produced their characteristic heads of fructification.

With regard to the precise nature of the spores and other cells present in various instances little can be said, as, unless their development were to be carefully followed out through all its stages, it is impossible to refer them to their correct species or even genera. The greater number of them are apparently referable to the old orders of fungi--_Sphaeronemei_, _Melanconei_, _Torulacei_, _Dematiei_, and _Mucedines_, while some probably belonged to the _Pucciniei_ and _Coaemacei_. Amongst those belonging to the _Torulacei_, the most interesting was a representative of the rare genus _Tetraploa_.

Distinct green algoid cells occurred in some specimens. Then follow in the report details of observations made on the rise and fall of diseases, of which diarrhoea, dysentery, cholera, ague, and dengue were selected and compared with the increase or diminution of atmospheric cells. The conclusions arrived at are:--

"Spores and other vegetable cells are constantly present in atmospheric dust, and usually occur in considerable numbers; the majority of them are living, and capable of growth and development.

The amount of them present in the air appears to be independent of conditions of velocity and direction of the wind, and their number is not diminished by moisture.

"No connection can be traced between the numbers of bacteria, spores, &c., present in the air, and the occurrence of diarrhoea, dysentery, cholera, ague, or dengue, nor between the presence or abundance of any special form or forms of cells, and the prevalence of any of these diseases.

"The amount of inorganic and amorphous particles and other debris suspended in the atmosphere is directly dependent on conditions of moisture and velocity of wind."

This report is accompanied by fourteen large and well-executed plates, each containing hundreds of figures of organic bodies collected from the air between February and September. It is valuable both for its evidence as to the number and character of the spores in the air, and also for the tables showing the relation between five forms of disease, and their fluctuations, as compared with the amount of spores floating in the atmosphere.

We are fain to believe that we have represented the influence of fungi on man as far as evidence seems to warrant. The presence of forms of mould in some of their incipient conditions in different diseased parts of the human body, externally and internally, may be admitted without the a.s.sumption that they are in any manner the cause of the diseased tissues, except in such cases as we have indicated. Hospital gangrene may be alluded to in this connection, and it is possible that it may be due to some fungus allied to the crimson spots (blood rain) which occur on decayed vegetation and meat in an incipient stage of decomposition. This fungus was at one time regarded as an algal, at another as animal; but it is much more probable that it is a low condition of some common mould. The readiness with which the spores of fungi floating in the atmosphere adhere to and establish themselves on all putrid or corrupt substances is manifest in the experience of all who have had to do with the dressing of wounds, and in this case it is a matter of the greatest importance that, as much as possible, atmospherical contact should be avoided.

Recently a case occurred at the Botanic Gardens at Edinburgh which was somewhat novel. The a.s.sistant to the botanical professor was preparing for demonstration some dried specimens of a large puff-ball, filled with the dust-like spores, which he accidentally inhaled, and was for some time confined to his room under medical attendance from the irritation they caused. This would seem to prove that the spores of some fungi are liable, when inhaled in large quant.i.ties, to derange the system and become dangerous; but under usual and natural conditions such spores are not likely to be present in the atmosphere in sufficient quant.i.ty to cause inconvenience. In the autumn a very large number of basidiospores must be present in the atmosphere of woods, and yet there is no reason to believe that it is more unhealthy to breathe the atmosphere of a wood in September or October than in January or May. Dreadful effects are said to be produced by a species of black rust which attacks the large South of Europe reed, _Arundo donax_. This is in all probability the same species with that which attacks _Arundo phragmitis_ in this country, the spores of which produce violent headaches and other disorders amongst the labourers who cut the reeds for thatching. M. Michel states that the spores from the parasite on _Arundo donax_, either inhaled or injected, produce violent papular eruption on the face, attended with great swelling, and a variety of alarming symptoms which it is unnecessary to particularize, in various parts of the body.[K] Perhaps if _Sarcina_ should ultimately prove to be a fungus, it may be added to the list of those which aggravate, if they are not the primary cause of, disease in the human subject.

II. What influences can be attributed to fungi upon animals other than man? Clearly instinct preserves animals from many dangers. It may be presumed that under ordinary circ.u.mstances there is not much fear of a cow or a sheep poisoning itself in a pasture or a wood. But under extraordinary circ.u.mstances it is not only possible, but very probable, that injuries may occur. For instance, it is well known that not only rye and wheat, but also many of the gra.s.ses, are liable to infection from a peculiar form of fungus called "ergot." In certain seasons this ergot is much more common than others, and the belief is strong in those who ought to know something of the subject from experience, viz., farmers and graziers, that in such seasons it is not uncommon for cattle to slip their young through feeding on ergotized gra.s.s. Then, again, it is fairly open to inquiry whether, in years when "red rust" and "mildew" are more than usually plentiful on gra.s.ses, these may not be to a certain extent injurious. Without attempting to a.s.sociate the cattle plague in any way with fungi on gra.s.s, it is nevertheless a most remarkable coincidence that the year in which the cattle disease was most prevalent in this country was one in which there was--at least in some districts--more "red rust" on gra.s.ses than we ever remember to have seen before or since; the clothes of a person walking through the rusty field soon became orange-coloured from the abundance of spores. Graziers on this point again seem to be generally agreed, that they do not think "red rust"

has been proved to be injurious to cattle. The direct influence of fungi on quadrupeds, birds, reptilia, &c., seems to be infinitesimally small.

Insects of various orders have been observed from time to time to become the prey of fungi.[L] That known at Guadaloupe under the name of _La Guepe Vegetale_, or vegetable wasp, has been often cited as evidence that, in some instances at least, the fungus attacks the insect whilst still living. Dr. Madianna states that he has noticed the wasp still living with its inc.u.mbrance attached to it, though apparently in the last stage of existence, and seeming about to perish from the influence of its destructive parasite.[M] This fungus is called by Tulasne _Torrubia sphecocephala_.[N] About twenty-five species of this genus of sphaeriaceous fungi have been described as parasitic on insects. Five species are recorded in South Carolina, one in Pennsylvania, found on the larvae of the May-bug, and one other North American species on Nocturnal Lepidoptera, one in Cayenne, one in Brazil, on the larva of a _Cicada_, and one on a species of ant, two in the West Indies, one in New Guinea on a species of _Coccus_, and one on a species of _Vespa_ in Senegal. In Australia two species have been recorded, and two are natives of New Zealand. Dr. Hooker found two in the Kha.s.sya mountains of India, and one American species has also been found at Darjeeling. It has long been known that one species, which has a medicinal repute there, is found in China, whilst three have been recorded in Great Britain. Opinions are divided as to whether in these instances the fungus causes or is subsequent to the death of the insect. It is generally the belief of entomologists that the death of the insect is caused by the fungus. In the case of _Isaria sphingum_, which is the conidia form of a species of _Torrubia_, the moth has been found standing on a leaf, as during life, with the fungus sprouting from its body.

Other and less perfect forms of fungi also attack insects. During the summer of 1826, Professor Sebert collected a great many caterpillars of _Arctia villica_, for the purpose of watching their growth. These insects on arriving at their full size became quite soft, and then suddenly died. Soon after they became hard, and, if bent, would easily break into two pieces. Their bodies were covered with a beautiful s.h.i.+ning white mould. If some of the caterpillars affected with the parasitic mould were placed on the same tree with those apparently free from its attack, the latter soon exhibited signs that they also were attacked in the same manner, in consequence of coming into contact with each other.[O]

During the spring of 1851, some twelve or twenty specimens were found from amongst myriads of _Cicada septemdecim_, which, though living, had the posterior third of the abdominal contents converted into a dry, powdery, ochreous-yellow compact ma.s.s of sporuloid bodies. The outer coverings of that portion of the insect were loose and easily detached, leaving the fungoid matter in the form of a cone affixed by its base to the unaffected part of the abdomen of the insect. The fungus may commence, says Dr. Leidy, its attacks upon the larva, develop its mycelium, and produce a sporular ma.s.s within the active pupa, when many are probably destroyed; but should some be only affected so far as not to destroy the organs immediately essential to life, they might undergo their metamorphosis into the imago, in which case they would be affected in the manner previously described.[P]

The common house-fly in autumn is very usually subject to the attacks of a mouldy fungus called _Sporendonema muscae_, or _Empusa muscae_ in former times, which is now regarded as the terrestrial condition of one of the _Saprolegniei_.[Q] The flies become sluggish, and at last fix themselves to some object on which they die, with their legs extended and head depressed, the body and wings soon becoming covered with a minute white mould, the joints of which fall on the surrounding object. Examples are readily distinguished when they settle on windows and thus succ.u.mb to their foe. Mr. Gray says that a similar mould has been observed on individuals of the wasp family.

A _Gryllotalpa_ was found in a wood near Newark, Delaware, U. S., upon turning over a log. The insect was seen standing very quietly at the mouth of its oval cell, which is formed in the earth, having a short curved tube to the surface. Upon taking it up it exhibited no signs of movement, though perfectly fresh and lifelike in appearance. On examining it next morning it still presented no signs of life. Every part of the insect was perfect, not even the antennae being broken.

Upon feeling it, it was very hard and resistant, and on making an incision through the thorax it exhaled a fungoid odour. The insect had been invaded by a parasitic fungus which everywhere filled the animal, occupying the position of all the soft tissue, and extending even into the tarsal joints. It formed a yellowish or cream-coloured compact ma.s.s.[R]

The destructive silk-worm disease, _Botrytis Ba.s.siana_, 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 sh.e.l.l, 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 pa.s.sed over, and that is the relation which they bear to some of the insect tribes in furnis.h.i.+ng 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 _aecidium_ 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 _Anguillidae_ revel in tufts of mould, and fleshy Agarics, as they pa.s.s 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 _Psocidae_ 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 a.s.similation 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 ma.s.s 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 const.i.tuents 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 relations.h.i.+p, change of composition; and all these changes are effected by various combined agencies--water, air, light, heat, these furnis.h.i.+ng 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 pa.s.sing, 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 s.m.u.t, for _Ustilago_ is as common in Asia and America as in Europe. We have seen it on numerous gra.s.ses 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 const.i.tuting 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 ma.s.s 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 gra.s.ses 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.