Therefore, that from the latter a decided form, or a mixture of several forms, is to be found sown on one spot, is no proof of their generic connection with one which has been sown for the purpose of experiments; and the matter will only be more confused if we call imagination to our aid, and place the forms which are found near one another, according to a real or fancied resemblance, in a certain series of development. All those statements on the sphere of form and connection, which have for their basis such a superficial work, and are not based on the clear exposition of the continuity of development, as by the origin of the connection of the _Mucor_ with _Penicillium_, _Oidium lactis_ and _Mucor_, _Oidium_ and _Penicillium_, are rejected as unfounded.

A source of error, which can also interfere in the last-named superficial method of cultivation for experiments, is, viz., that heterogeneous unwished-for spores intrude themselves from without, among the seed which is sown, but that has been until now quite disregarded. It is of great importance in practice, but in truth, for our present purpose, synonymous with what we have already written.

Those learned in the science of this kind of culture lay great stress on its importance, and many apparatuses have been constructed, called "purely cultivating machines," for the purpose of destroying the spores which are contained in the substratum, and preventing the intrusion of those from without. The mixture in the seed which is sown has of course not been obviated. These machines may, perhaps, in every other respect, fulfil their purpose, but they cannot change the form of the question, and the most ingeniously constructed apparatus cannot replace the attention and intellect of the observer.[B]

Two distinct kinds of phenomena have been grouped under the term "polymorphy." In one series two or more forms of fruit occur consecutively or simultaneously on the same individual, and in the other two or more forms appear on a different mycelium, on a different part of the same plant, or on a matrix wholly distinct and different; in the latter case the connection being attested or suspected circ.u.mstantially, in the former proved by the method suggested by De Bary. It will at once be conceded that in cases where actual growth and development substantiate the facts the polymorphy is undoubted, whilst in the other series it can at best be little more than suspected. We will endeavour to ill.u.s.trate both these series by examples.

One of the first and earliest suspected cases of dualism, which long puzzled the older mycologists, was observed amongst the Uredines, and many years ago it was held that there must be some mysterious a.s.sociation between the "red rust" (_Trichobasis ruligo vera_) of wheat and gra.s.ses and the "corn mildew" (_Puccinia graminis_) which succeeded it. The simple spored rust first makes its appearance, and later the bilocular "mildew." It is by no means uncommon to find the two forms in the same pustule. Some have held, without good reason, that the simple cells became afterwards divided and converted into _Puccinia_, but this is not the case; the uredo-spores are always simple, and remain so except in _Uredo linearis_, where every intermediate stage has been observed. Both are also perfect in their kind, and capable of germination.

What the precise relations between the two forms may be has as yet never been revealed to observers, but that the two forms belong to one species is not now doubted. Very many species of _Puccinia_ have already been found a.s.sociated with a corresponding _Trichobasis_, and of _Phragmidium_ with a relative _Lecythea_, but it may be open to grave doubt whether some of the very many species a.s.sociated by authors are not so cla.s.sed upon suspicion rather than observation. We are ready to admit that the evidence is strong in favour of the dimorphism of a large number of species--it _may_ be in all, but this awaits proof, or substantial presumption on good grounds. Up to the present we know that there are species of _Trichobasis_ which have never been traced to a.s.sociation with a _Puccinia_, and doubtless there will be species of _Puccinia_ for which no corresponding _Uredo_ or _Trichobasis_ can be found.

Tulasne remarks, in reference to _Puccinia sonchi_, in one of his memoirs, that this curious species exhibits, in effect, that a _Puccinia_ may unite three sorts of reproductive bodies, which, taking part, const.i.tute for the mycologists of the day three entirely different plants--a _Trichobasis_, a _Uromyces_, and a _Puccinia_. The Uredines are not less rich, he adds, in reproductive bodies of divers sorts than the _Pyrenomycetes_ and the _Discomycetes_; and we should not be surprised at this, since it seems to be a law, almost constant in the general harmony of nature, that the smaller the organized beings are, the more their races are prolific.

In _Puccinia variabilis_, Grev., it is common to find a unicellular form, species of _Trichobasis_, in the same pustules. A like circ.u.mstance occurs with _Puccinia violarum_, Link., and _Trichobasis violarum_, B.; with _Puccinia fallens_, C., and _Trichobasis fallens_, Desm.; also with _Puccinia menthae_, P., and _Trichobasis l.a.b.i.atarum_, D. C. In _Melampsora_, again, the prismatic pseudospores of _Melampsora salicina_, Lev., are the winter fruits of _Lecythea caprearum_, Lev., as those of _Melampsora populina_, Lev., are of _Lecythea populina_, Lev. In the species of _Lecythea_ themselves will be found, as De Bary[C] has shown, hyaline cysts of a larger size, which surround the pseudospores in the pustules in which they are developed.

A good ill.u.s.tration of dimorphism in one of the commonest of moulds is given by De Bary in a paper from which we have already quoted.[D] He writes thus:--In every household there is a frequent unbidden guest, which appears particularly on preserved fruits, viz., the _mould_ which is called _Aspergillus glaucus_. It shows itself to the naked eye as a woolly floccy crust over the substance, first purely white, then gradually covered with little fine glaucous, or dark green dusty heads. More minute microscopical examination shows that the fungus consists of richly ramified fine filaments, which are partly disseminated in the substratum, and partly raised obliquely over it.

They have a cylindrical form with rounded ends, and are divided into long outstretched members, each of which possesses the property which legitimatizes it as a vesicle in the ordinary sense of the word; it contains, enclosed within a delicate structureless wall, those bodies which bear the appearance of a finely granulated mucous substance, which is designated by the name of protoplasm, and which either equally fills the cells, or the older the cell the more it is filled with watery cavities called vacuoles.

All parts are at first colourless. The increase in the length of the filaments takes place through the preponderating growth near their points; these continually push forward, and, at a short distance from them, successive new part.i.tions rise up, but at a greater distance, the growth in the length ceases. This kind of growth is called point growth. The twigs and branches spring up as lateral dilatations of the princ.i.p.al filament, which, once designed, enlarges according to the point growth. This point growth of every branch is, to a certain extent, unlimited. The filaments in and on the substratum are the first existing members of the fungus; they continue so long as it vegetates. As the parts which absorb nourishment from and consume the substance, they are called the _mycelium_. Nearly every fungus possesses a mycelium, which, without regard to the specific difference of form and size, especially shows the described nature in its construction and growth.

The superficial threads of the mycelium produce other filaments beside those numerous branches which have been described, and which are the fruit thread (carpoph.o.r.e) or conidia thread. These are on an average thicker than the mycelium threads, and only exceptionally ramified or furnished with part.i.tions; they rise almost perpendicularly into the air, and attain a length of, on an average, half a millimetre, or one-fiftieth of an inch, but they seldom become longer, and then their growth is at an end. Their free upper end swells in a rounded manner, and from this is produced, on the whole of its upper part, rayed divergent protuberances, which attain an oval form, and a length almost equal to their radius, or, in weaker specimens, the diameter of the rounded head. The rayed divergent protuberances are the direct producers and bearers of the propagating cells, spores, or conidia, and are called sterigmata. Every sterigma at first produces at its point a little round protuberance, which, with a strong narrow basis, rests upon the sterigma. These are filled with protoplasm, swell more and more, and, after some time, separate themselves by a part.i.tion from the sterigma into independent cells, spores, or conidia.

The formation of the first spore takes place at the same end of the sterigma, and in the same manner a second follows, then a third, and so on; every one which springs up later pushes its predecessor in the direction of the axis of the sterigma in the same degree in which it grows itself; every successive spore formed from a sterigma remains for a time in a row with one another. Consequently every sterigma bears on its apex a chain of spores, which are so much the older, the farther they stand from the sterigma. The number of the links in a chain of spores reaches in normal specimens to ten or more. All sterigmata spring up at the same time, and keep pace with one another in the formation of the spores. Every spore grows for a time, according to its construction, and at last separates itself from its neighbours. The ma.s.s of dismembered spores forms that fine glaucous hue which is mentioned above. The spores, therefore, are articulated in rows, one after the other, from the ends of the sterigmata. The ripe spore, or conidium, is a cell of a round or broadly oval form, filled with a colourless protoplasm, and, if observed separately, is found to be provided with a brownish, finely verruculose, dotted wall.

[Ill.u.s.tration: FIG. 102.--_a._ _Aspergillus glaucus_; _b._ conidia; _c._ germinating conidium; _d._ conceptacle of _Eurotium_; _e._ ascus.]

The same mycelium which forms the pedicel for the conidia when it is near the end of its development, forms by normal vegetation a second kind of fructification. It begins as delicate thin little branches, which are not to be distinguished by the naked eye, and which mostly in four or six turns, after a quickly terminated growth, wind their ends like a corkscrew. (Fig. 102.) The sinuations decrease in width more and more, till they at last reach close to one another, and the whole end changes from the form of a corkscrew into that of a hollow screw. In and on that screw-like body, a change of a complicated kind takes place, which is a productive process. In consequence of this, from the screw body a globose receptacle is formed, consisting of a thin wall of delicate cells, and a closely entwined row of cells surrounded by this dense ma.s.s (_d_). By the enlargement of all these parts the round body grows so much, that by the time it is ripe it is visible to the naked eye. The outer surface of the wall a.s.sumes a compactness and a bright yellow colour; the greater part of the cells of the inner ma.s.s become asci for the formation of sporidia, while they free themselves from the reciprocal union, take a broad oval form, and each one produces within its inner s.p.a.ce eight sporidia (_e_). These soon entirely fill the ascus. When they are quite ripe, the wall of the conceptacle becomes brittle, and from irregular fissures, arising easily from contact, the colourless round sporidia are liberated.

The pedicels of both kinds of fruit are formed from the same mycelium in the order just described. If we examine attentively, we can often see both springing up close to one another from the same filament of a mycelium. This is not very easy in the close interlacing of the stalks of a ma.s.s of fungi in consequence of their delicacy and fragility.

Before their connection was known, the conceptacles and the conidia pedicels were considered as organs of two very different species of fungi. The conceptacles were called _Eurotium herbariorum_, and the conidia bearers were called _Aspergillus glaucus_.

Allied to _Eurotium_ is the group of _Erysiphei_, in which well-authenticated polymorphy prevails. These fungi are developed on the green parts of growing plants, and at first consist of a white mouldy stratum, composed of delicate mycelium, on which erect threads are produced, which break up into subglobose joints or conidia. The species on gra.s.s was named _Oidium monilioides_ before its relationship was known, but undoubtedly this is only the conidia of _Erysiphe graminis_. In like manner the vine disease (_Oidium Tuckeri_) is most probably only the conidia of a species of _Erysiphe_, of which the perfect condition has not yet been discovered. On roses the old _Oidium leucoconium_ is but the conidia of _Sphaerotheca pannosa_, and so of other species. The _Erysiphe_ which ultimately appears on the same mycelium consists of globose perithecia, externally furnished with thread-like appendages, and internally with asci containing sporidia. In this genus there are no less than five different forms of fruit,[E] the multiform threads on the mycelium, already alluded to as forms of _Oidium_, the asci contained in the sporangia, which is the proper fruit of the _Erysiphe_, larger stylospores which are produced in other sporangia, the smaller stylospores which are generated in the pycnidia, and separate sporules which are sometimes formed in the joints of the necklaces of the conidia. These forms are figured in the "Introduction to Cryptogamic Botany" from _Sphaerotheca Castagnei_, which is the hop mildew.[F] The vine disease, hop mildew, and rose mildew, are the most destructive species of this group, and the constant annoyance of cultivators.

[Ill.u.s.tration: FIG. 103.--_Erysiphe cichoracearum._ _a._ Receptacle; _o._ mycelium. (De Bary.)]

When first describing an allied fungus found on old paper, and named _Ascotricha chartarum_, the Rev. M. J. Berkeley called attention to the presence of globose conidia attached to the threads which surround the conceptacles,[G] and this occurred as long since as 1838. In a recent species of _Chaetomium_ found on old sacking, _Chaetomium griseum_, Cooke,[H] we have found tufts in all respects similar externally to the _Chaetomium_, but no perithecium was formed, naked conidia being developed apparently at the base of the coloured threads. In _Chaetomium funicolum_, Cooke, a black mould was also found which may possibly prove to be its conidia, but at present there is no direct evidence.

The brothers Tulasne have made us acquainted with a greater number of instances amongst the _Sphaeriacei_ in which multiple organs of reproduction prevail. Very often old and decaying individuals belonging to species of _Boletus_ will be found filled, and their entire substance internally replaced, by the threads and mult.i.tudinous spores of a golden yellow parasite, to which the name of _Sepedonium chrysospermum_ has been given.

According to Tulasne, this is merely a condition of a sphaeriaceous fungus belonging to his genus _Hypomyces_.[I]

The same observers also first demonstrated that _Trichoderma viride_, P., was but the conidia-bearing stage of _Hypocrea rufa_, P., another sphaeriaceous fungus. The ascigerous stroma of the latter is indeed frequently a.s.sociated in a very close manner with the cushions of the pretended _Trichoderma_, or in other cases the same stroma will give rise to a different apparatus of conidia, of which the princ.i.p.al elements are acicular filaments, which are short, upright, and almost simple, and which give rise to small oval conidia which are solitary on the tips of the threads. Therefore this _Hypocrea_ will possess two different kinds of conidia, as is the case in many species of _Hypomyces_.

A most familiar instance of dualism will be found in _Nectria cinnabarina_, of which the conidia form is one of the most common of fungi, forming little reddish nodules on all kinds of dead twigs.[J]

[Ill.u.s.tration: FIG. 104.--Twig with _Tubercularia_ on the upper portion, _Nectria_ on the lower.]

Almost any small currant twig which has been lying on the ground in a damp situation will afford an opportunity of studying this phenomenon.

The whole surface of the twig will be covered from end to end with little bright pink prominences, bursting through the bark at regular distances, scarcely a quarter of an inch apart. Towards one end of the twig probably the prominences will be of a deeper, richer colour, like powdered cinnabar. The naked eye is sufficient to detect some difference between the two kinds of pustules, and where the two merge into each other specks of cinnabar will be visible on the pink projections. By removing the bark it will be seen that the pink bodies have a sort of paler stem, which spreads above into a somewhat globose head, covered with a delicate mealy bloom. At the base it penetrates to the inner bark, and from it the threads of mycelium branch in all directions, confined, however, to the bark, and not entering the woody tissues beneath. The head, placed under examination, will be found to consist of delicate parallel threads compacted together to form the stem and head. Some of these threads are simple, others are branched, bearing here and there upon them delicate little bodies, which are readily detached, and which form the mealy bloom which covers the surface. These are the conidia, little slender cylindrical bodies, rounded at the ends.

[Ill.u.s.tration: FIG. 105.--Section of _Tubercularia_. _c._ Threads with conidia.[K]]

Pa.s.sing to the other bodies, which are of a deeper colour, it will soon be discovered that, instead of being simple rounded heads, each tubercle is composed of numerous smaller, nearly globose bodies, closely packed together, often compressed, all united to a base closely resembling the base of the other tubercles. If for a moment we look at one of the tubercles near the spot where the crimson tubercles seem to merge into the pink, we shall not only find them particoloured, but that the red points are the identical globose little heads just observed in cl.u.s.ters. This will lead to the suspicion, which can afterwards be verified, that the red heads are really produced on the stem or stroma of the pink tubercles.

A section of one of the red tubercles will show us how much the internal structure differs. The little subglobose bodies which spring from a common stroma or stem are hollow sh.e.l.ls or capsules, externally granular, internally filled with a gelatinous nucleus. They are, indeed, the perithecia of a sphaeriaceous fungus of the genus _Nectria_, and the gelatinous nucleus contains the fructification.

Still further examination will show that this fructification consists of cylindrical asci, each enclosing eight elliptical sporidia, closely packed together, and mixed with slender threads called paraphyses.

Here, then, we have undoubted evidence of _Nectria cinnabarina_, with its fruit, produced in asci growing from the stroma or stem, and in intimate relationship with what was formerly named _Tubercularia vulgaris_. A fungus with two forms of fruit, one proper to the pink, or _Tubercularia_ form, with naked slender conidia, the other proper to the mature fungus, enclosed in asci, and generated within the walls of a perithecium. Instances of this kind are now known to be far from uncommon, although they cannot always, or often, be so clearly and distinctly traced as in the ill.u.s.tration which we have selected.

[Ill.u.s.tration: FIG. 106.--D. _Nectria_ surrounding _Tubercularia_; E.

tuft of _Nectria cinnabarina_; F. section of stroma; G. ascus and paraphyses.]

It is not uncommon for the conidia of the _Sphaeria_ to partake of the characteristics of a mould, and then the perithecia are developed amongst the conidial threads. A recently recorded instance of this relates to _Sphaeria Epochnii_, B. and Br.,[L] the conidia form of which was long known before the _Sphaeria_ related to it was discovered, under the name of _Epochnium fungorum_. The _Epochnium_ forms a thin stratum, which overruns various species of _Corticium_.

The conidia are at first uniseptate. The perithecia of the _Sphaeria_ are at first pale bottle-green, crowded in the centre of the _Epochnium_, then black green granulated, sometimes depressed at the summit, with a minute pore. The sporidia are strongly constricted in the centre, at first uniseptate, with two nuclei in each division.

Another _Sphaeria_ in which the a.s.sociation is undoubted is the _Sphaeria aquila_, Fr.,[M] which is almost always found nestling in a woolly brown subiculum, for the most part composed of barren brown jointed threads. These threads, however, produce, under favourable conditions, mostly before the perfection of the perithecia, minute subglobose conidia, and in this state const.i.tute what formerly bore the name of _Sporotrichum fusc.u.m_, Link., but now recognized as the conidia of _Sphaeria aquila_.

In _Sphaeria nidulans_, Schw., a North American species, we have more than once found the dark brown subiculum bearing large triseptate conidia, having all the characters of the genus _Helminthosporium_. In _Sphaeria pilosa_, P., Messrs. Berkeley and Broome have observed oblong conidia, rather irregular in outline, terminating the hairs of the perithecium.[N] The same authors have also figured the curious pentagonal conidia springing from flexuous threads accompanying _Sphaeria felina_, Fckl.,[O] and also the threads resembling those of a _Cladotrichum_ with the angular conidia of _Sphaeria cupulifera_, B.

and Br.[P] A most remarkable example is also given by the Brothers Tulasne in _Pleospora polytricha_, in which the conidia-bearing threads not only surround, but grow upon the perithecia, and are crowned by fascicles of septate conidia.[Q]

Instances of this kind have now become so numerous that only a few can be cited as examples of the rest. It is not at all improbable that the majority of what are now cla.s.sed together as species under the genus of black moulds, _Helminthosporium_, will at some not very distant period be traced as the conidia of different species of ascomycetous fungi. The same fate may also await other allied genera, but until this a.s.sociation is established, they must keep the rank and position which has been a.s.signed to them.

Another form of dualism, differing somewhat in character from the foregoing, finds ill.u.s.tration in the sphaeriaceous genus _Melanconis_, of Tulasne, in which the free spores are still called conidia, though in most instances produced in a sort of spurious conceptaculum, or borne on short threads from a kind of cushion-shaped stroma. In the _Melanconis stilbostoma_,[R] there are three forms, one of slender minute bodies, oozing out in the form of yellow tendrils, which may be spermatia, formerly called _Nemaspora crocea_. Then there are the oval brown or olive brown conidia, which are at first covered, then oozing out in a black pasty ma.s.s, formerly _Melanconium bicolor_, and finally the sporidia in asci of _Sphaeria stilbostoma_, Fries. In _Melanconis Berkeleii_, Tul., the conidia are quadrilocular, previously known as _Stilbospora macrosperma_, B. and Br. In a closely-allied species from North America, _Melanconis bicornis_, Cooke, the appendiculate sporidia are similar, and the conidia would also appear to partake of the character of _Stilbospora_. We may remark here that we have seen a brown mould, probably an undescribed species of _Dematiei_, growing in definite patches around the openings in birch bark caused by the crumpent ostiola of the perithecia of _Melanconis stilbostoma_, from the United States.

In _Melanconis lanciformis_,[S] Tul., there are, it would appear, four forms of fruit. One of these consists of conidia, characterized by Corda as _Coryneum disciforme_.[T] Stylospores, which are also figured by Corda under the name of _Coniothecium betulinum_; pycnidia,[U] first discovered by Berkeley and Broome, and named by them _Hendersonia polycystis_;[V] and the ascophorous fruits which const.i.tuted the _Sphaeria lanciformis_ of Fries. Mr. Currey indicated _Hendersonia polycystis_, B. and Br., as a form of fruit of this species in a communication to the Royal Society in 1857.[W] He says this plant grows upon birch, and is in perfection in very moist weather, when it may be recognized by the large black soft gelatinous protuberances on the bark, formed by spores escaping and depositing themselves upon and about the apex of the perithecium.

This I suspect to be an abnormal state of a well-known Sphaeria (_S.

lanciformis_), which grows upon birch, and upon birch only.

We might multiply, almost indefinitely, instances amongst the _Sphaeriacei_, but have already given sufficient for ill.u.s.tration, and will therefore proceed briefly to notice some instances amongst the _Discomycetes_, which also bear their complete or perfect fruit in asci.

The beautiful purple stipitate cups of _Bulgaria sarcoides_, which may be seen flourishing in the autumn on old rotten wood, are often accompanied by club-shaped bodies of the same colour; or earlier in the season these clavate bodies may be found alone, and at one time bore the name of _Tremella sarcoides_. The upper part of these clubs disseminate a great abundance of straight and very slender spermatia.

Earlier than this they are covered with globose conidia. The fully-matured _Bulgaria_ develops on its hymenium clavate delicate asci, each enclosing eight elongated hyaline sporidia, so that we have three forms of fruit belonging to the same fungus, viz. conidia and spermatia in the _Tremella_ stage, and sporidia contained in asci in the mature condition.[X] The same phenomena occur with _Bulgaria purpurea_, a larger species with different fruit, long confounded with _Bulgaria sarcoides_.

On the dead stems of nettles it is very common to meet with small orange tubercles, not much larger than a pin's head, which yield at this stage a profusion of slender linear bodies, produced on delicate branched threads, and at one time bore the name of _Dacrymyces Urticae_, but which are now acknowledged to be only a condition of a little tremelloid _Peziza_ of the same size and colour, which might be mistaken for it, if not examined with the microscope, but in which there are distinct asci and sporidia. Both forms together are now regarded as the same fungus, under the name of _Peziza fusarioides_, B.

The other series of phenomena grouped together under the name of polymorphism relate to forms which are removed from each other, so that the mycelium is not identical, or, more usually, produced on different plants. The first instance of this kind to which we shall make reference is one of particular interest, as ill.u.s.trative of the old popular creed, that berberry bushes near corn-fields produced mildewed corn. There is a village in Norfolk, not far from Great Yarmouth, called "Mildew Rollesby," because of its unenviable notoriety in days past for mildewed corn, produced, it was said, by the berberry bushes, which were cut down, and then mildew disappeared from the corn-fields, so that Rollesby no longer merited its _sobriquet_. It has already been shown that the corn-mildew (_Puccinia graminis_) is dimorphous, having a one-celled fruit (_Trichobasis_), as well as a two-celled fruit (_Puccinia_). The fungus which attacks the berberry is a species of cl.u.s.ter-cup (_aecidium berberidis_), in which little cup-like peridia, containing bright orange pseudospores, are produced in tufts or cl.u.s.ters on the green leaves, together with their spermogonia.

De Bary's observations on this a.s.sociation of forms were published in 1865.[Y] In view of the popular belief, he determined to sow the spores of _Puccinia graminis_ on the leaves of the berberry. For this purpose he selected the septate resting spores from _Poa pratensis_ and _Tritic.u.m repens_. Having caused the spores to germinate in a moist atmosphere, he placed fragments of the leaves on which they had developed their secondary spores on young but full-grown berberry leaves, under the same atmospheric conditions. In from twenty-four to forty-eight hours a quant.i.ty of the germinating threads had bored through the walls and penetrated amongst the subjacent cells. This took place both on the upper and under surface of the leaves. Since, in former experiments, it appeared that the spores would penetrate only in those cases where the plant was adapted to develop the parasite, the connection between _P. graminis_ and _aecid. berberidis_ seemed more than ever probable. In about ten days the spermogonia appeared. After a time the cut leaves began to decay, so that the fungus never got beyond the spermogonoid stage. Some three-year-old seedlings were then taken, and the germinating resting spores applied as before. The plants were kept under a bell-gla.s.s from twenty-four to forty-eight hours, and then exposed to the air like other plants. From the sixth to the tenth day, yellow spots appeared, with single spermogonia; from the ninth to the twelfth, spermogonia appeared in numbers on either surface; and, a few days later, on the under surface of the leaves, the cylindrical sporangia of the _aecidium_ made their appearance, exactly as in the normally developed parasite, except that they were longer, from being protected from external agents. The younger the leaves, the more rapid was the development of the parasite, and sometimes, in the younger leaves, the luxuriance was far greater than in free nature. Similar plants, to the number of two hundred, were observed in the nursery, and though some of them had _aecidium_ pustules, not one fresh pustule was produced; while two placed under similar circ.u.mstances, but without the application of any resting spores, remained all the summer free from _aecidium_. It seems, then, indubitable so far that _aecidium berberidis_ does spring from the spores of _Puccinia graminis_.

It has, however, to be remarked that De Bary was not equally successful in producing the _Puccinia_ from the spores of the _aecidium_. In many cases the spores do not germinate when placed on gla.s.s, and they do not preserve their power of germinating very long.

He reverts then to the evidence of experiments inst.i.tuted by agriculturists. Bonninghausen remarked, in 1818, that wheat, rye, and barley which were sown in the neighbourhood of a berberry bush covered with _aecidium_ contracted rust immediately after the maturation of the spores of the _aecidia_. The rust was most abundant where the wind carried the spores. The following year the same observations were repeated; the spores of the _aecidium_ were collected, and applied to some healthy plants of rye. After five or six days these plants were affected with rust, while the remainder of the crop was sound. In 1863 some winter rye was sown round a berberry bush, which in the following year was infested with _aecidium_, which was mature in the middle of May, when the rye was completely covered with rust. Of the wild gra.s.ses near the bush, _Tritic.u.m repens_ was most affected. The distant plants of rye were free from rust.

[Ill.u.s.tration: FIG. 107.--Cells and pseudospores of _aecidium berberidis_.]

The spores of the _aecidium_ would not germinate on berberry leaves; the berberry _aecidium_ could not therefore spring from the previous _aecidium_. The uredospores of _Puccinia graminis_ on germinating penetrate into the parenchym of the gra.s.s on which they are sown; but on berberry leaves, if the tips of the threads enter for a short distance into the stomates their growth at once ceases, and the leaves remain free from parasites.

[Ill.u.s.tration: FIG. 108.--Cells and pseudospores of _aecidium graveolens_.]

Montagne has, however, described a _Puccinia berberidis_ on leaves of _Berberis glauca_ from Chili, which grows in company with _aecidium berberidis_. This at first sight seems to contradict the above conclusions; but the _aecidium_ which from the same disc produces the puccinoid resting spores, appears to be different from the European species, inasmuch as the cells of the wall of the sporangium are twice as large, and the spores decidedly of greater diameter.[Z] The resting spores, moreover, differ not only from those of _Puccinia graminis_, but from those of all other European species.

From this account, then, it is extremely probable that the _aecidium_ of the berberry enters into the cycle of existence of _Puccinia graminis_, and, if this be true, wherefore should not other species of _Puccinia_ be related in like manner to other _aecidia_? This is the conclusion to which many have arrived, and, taking advantage of certain presumptions, have, we fear, rashly a.s.sociated many such forms together without substantial evidence. On the leaves of the primrose we have commonly a species of _aecidium_, _Puccinia_, and _Uromyces_ nearly at the same time; we may imagine that all these belong to one cycle, but it has not yet been proved. Again, _Uromyces cacaliae_, Unger, _Uredo cacaliae_, Unger, and _aecidium cacaliae_, Thumen, are considered by Heufler[a] to form one cycle. Numerous others are given by f.u.c.kel,[b] and De Bary, in the same memoir from which we have already cited, notes _Uromyces appendiculatus_, Link., _U. phaseolorum_, Tul., and _Puccinia tragopogonis_, Ca., as possessing five kinds of reproductive organs. Towards the end of the year, shortly stipitate spores appear on their stroma, which do not fall off. These spores, which do not germinate till after a shorter or longer winter rest, may conveniently be called resting spores, or, as De Bary calls them, _teleutospores_, being the last which are produced. These at length germinate, become articulated, and produce ovate or kidney-shaped spores, which in their turn germinate, penetrating the cuticle of the mother plant, avoiding the stomates or apertures by which it breathes. After about two or three weeks, the mycelium, which has ramified among the tissues, produces an _aecidium_, with its constant companion, spermogonia--distinct cysts, that is, from which a quant.i.ty of minute bodies ooze out, often in the form of a tendril, the function of which is imperfectly known at present, but which from a.n.a.logy we regard as a form of fruit, though it is just possible that they may be rather of the nature of spermatozoids. The _aecidia_ contain, within a cellular membranous sac, a fructifying disc, which produces necklaces of spores, which ultimately separate from each other in the form of a granular powder.