The grains of which it is composed germinate in their turn, no longer avoiding the stomates as before, but penetrating through their aperture into the parenchym. The new resultant mycelium reproduces the _Uredo_, or fifth form of fructification, and the _Uredo_ spores fall off like those of the _aecidium_, and in respect of germination, and mode of penetration, present precisely the same phenomena. The disc which has produced the _Uredo_ spores now gives rise to the resting spores, and so the cycle is complete.[c]

The late Professor Oersted, of Copenhagen, was of opinion that he had demonstrated the polymorphy of the Tremelloid Uredines, and satisfied himself that the one condition known as _Podisoma_ was but another stage of _Roestelia_.[d] Some freshly gathered specimens of _Gymnosporangium_ were damped with water, and during the night following the spores germinated profusely, so that the teleutospores formed an orange-coloured powder. A little of this powder was placed on the leaves of five small sorbs, which were damped and placed under bell-gla.s.ses. In five days yellow spots were seen on the leaves, and in two days more indications of spermogonia. The spermatia were discharged, and in two months from the first sowing, the peridia of _Roestelia_ appeared, and were developed.

"This trial of spores," says Oersted, "has conduced to the result expected, and proves that the teleutospores of _Gymnosporangium_, when transported upon the sorb, give rise to a totally different fungus, the _Roestelia cornuta_, that is to say, that an alternate generation comes between these fungi. They appertain in consequence to a single species, and the _Gymnosporangium_ ceased to be an independent species, and must be considered as synonymous with the first generation of _Roestelia_. The spores have been transported upon young shoots of the juniper-tree, and have now commenced to produce some mycelium in the bark. There is no doubt that in next spring it will result in _Gymnosporangium_."

Subsequently the same learned professor inst.i.tuted similar experiments upon other hosts, with the spores of _Podisoma_, and from thence he concluded that _Roestelia_ and _Podisoma_, in all their known species, were but forms the one of the other. Hitherto we are not aware that these results have been confirmed, or that the sowing of the spores of _Roestelia_ on juniper resulted in _Podisoma_. Such experiments should be received always with care, and not too hastily accepted in their apparent results as proven facts. Who shall say that _Roestelia_ would not have appeared on _Sorbus_ within two months without the sowing of _Podisoma_ spores?--because it is not by any means uncommon for that fungus to appear upon that plant. It is true many mycologists write and speak of _Roestelia_ and _Podisoma_ (or _Gymnosporangium_) as identical; but, as we think, without the evidence being so complete as to be beyond suspicion. It is, nevertheless, a curious fact that in Europe the number of species of _Roestelia_ and _Podisoma_ are equal, if one species be excluded, which is certainly not a good _Podisoma_, for the reception of which a new genus has been proposed.[e]

Amongst the ascigerous fungi will be found a curious but interesting genus formerly called _Cordyceps_, but for which Tulasne, in consequence of the discovery of secondary forms of fruit, has subst.i.tuted that of _Torrubia_.[f] These curious fungi partake more or less of a clavate form, and are parasitic on insects. The pupae of moths are sometimes seen bearing upon them the white branched mould, something like a _Clavaria_ in appearance, to which the name of _Isaria farinosa_ has been given. According to Tulasne, this is the conidia form of the bright scarlet, club-shaped body which is also found on dead pupae, called _Torrubia militaris_. An American mould of the same genus, _Isaria sphingum_, found on mature moths,[g] is in like manner declared to be the conidia of _Torrubia sphingum_; whereas a similar mould, found on dead spiders, called _Isaria arachnophila_,[h] is probably of a similar nature. An allied kind of compact mould, which is parasitic on _Cocci_, on the bark of trees, recently found in England by Mr. C. E. Broome, and named _Microcera coccophila_,[i] is said by Tulasne to be a condition of _Sphaerostilbe_, and it is intimated that other productions of a similar character bear like relations to other sphaeriaceous fungi.

For many species of _Torrubia_ no corresponding conidia are yet known.

Some instances might be noted, not without interest, in which the facts of dimorphism or polymorphism have not been satisfactorily proved, but final judgment is held in suspense until suspicion is replaced by conviction. Some years since, a quant.i.ty of dead box leaves were collected, on which flourished at the time a mould named _Penicillium roseum_. This mould has a roseate tint, and occurs in patches on the dead leaves lying upon the ground; the threads are erect and branched above, bearing chains of oblong, somewhat spindle-shaped spores, or, perhaps more accurately, conidia. When collected, these leaves were examined, and nothing was observed or noted upon them except this _Penicillium_. After some time, certainly between two and three years, during which period the box remained undisturbed, circ.u.mstances led to the examination again of one or two of the leaves, and afterwards of the greater number of them, when the patches of _Penicillium_ were found to be intermixed with another mould of a higher development, and far different character. This mould, or rather _Mucor_, consists of erect branching threads, many of the branches terminating in a delicate globose, gla.s.sy head, or sporangium, containing numerous very minute subglobose sporidia. This species was named _Mucor hyalinus_.[j] The habit is very much like that of the _Penicillium_, but without any roseate tint. It is almost certain that the _Mucor_ could not have been present when the _Penicillium_ was examined, and the leaves on which it had grown were enclosed in the tin box, but that the _Mucor_ afterwards appeared on the same leaves, sometimes from the same patches, and, as it would appear, from the same mycelium. The great difference in the two species lies in the fructification. In the _Penicillium_, the spores are naked, and in moniliform threads; whilst in _Mucor_ the spores are enclosed within globose membraneous heads or sporangia. Scarcely can we doubt that the _Mucor_ alluded to above, found thus intermixed, under peculiar circ.u.mstances, with _Penicillium roseum_, is no other than the higher and more complete form of that species, and that the _Penicillium_ is only its conidiiferous state. The presumption in this case is strong, and not so open to suspicion as it would be did not a.n.a.logy render it so extremely probable that such is the case, apart from the fact of both forms springing from the same ma.s.s of mycelium.

In such minute and delicate structures it is very difficult to manipulate the specimens so as to arrive at positive evidence. If a filament of mycelium could be isolated successfully, and a fertile thread, bearing the fruit of each form, could be traced from the same individual mycelium thread, the evidence would be conclusive. In default of such conclusive evidence, we are compelled to rest with a.s.sumption until further researches enable us to record the a.s.sumption as fact.[k]

Apropos of this very connection of _Penicillium_ with _Mucor_, a similar suspicion attaches to an instance noted by a wholly disinterested observer to this effect. "On a preparation preserved in a moist chamber, on the third day a white speck was seen on the surface, consisting of innumerable 'yeast' cells, with some filaments, branching in all directions. On the fourth day tufts of _Penicillium_, had developed two varieties--_P. glauc.u.m_ and _P. viride_. This continued until the ninth day, when a few of the filaments springing up in the midst of the _Penicillium_ were tipped with a dewdrop-like dilatation, excessively delicate--a mere distended pellicle. In some cases they seemed to be derived from the same filament as others bearing the ordinary branching spores of _Penicillium_, but of this I could not be positive. This kind of fructification increased rapidly, and on the fourteenth day spores had undoubtedly developed within the pellicle, just as had been observed in a previous cultivation, precisely similar revolving movements being also manifested."[l]

Although we have here another instance of _Mucor_ and _Penicillium_ growing in contact, the evidence is insufficient to warrant more than a suspicion of their ident.i.ty, inasmuch as the equally minute spores of _Mucor_ and _Penicillium_ might have mingled, and each producing its kind, no relationship whatever have existed between them, except their development from the same matrix.

Another case of a.s.sociation--for the evidence does not proceed further--was recorded by us, in which a dark-coloured species of _Penicillium_ was closely a.s.sociated with what we now believe to be a species of _Macrosporium_--but then designated a _Sporidesmium_--and a minute _Sphaeria_ growing in succession on damp wall-paper. a.s.sociation is all that the _facts_ warrant us in calling it.

We cannot forbear alluding to one of the species of _Sphaeria_ to which Tulasne[m] attributes a variety of forms of fruit, and we do so here because we think that a circ.u.mstance so extraordinary should be confirmed before it is accepted as absolutely true. This refers to the common _Sphaeria_ found on herbaceous plants, known as _Sphaeria_ (_Pleospora_) _herbarum_. First of all the very common mould called _Cladosporium herbarum_ is const.i.tuted as conidia, and of this again _Macrosporium sarcinula_, Berk., is considered to be another condition. In the next place, _Cytispora orbicularis_, Berk., and _Phoma herbarum_, West., are regarded as pycnidia, enclosing stylospores. Then _Alternaria tenuis_, Pr.,[n] which is said to be parasitic on _Cladosporium herbarum_, is held to be only a form of that species, so that here we have (including the _perithecia_) no less than six forms or phases for the same fungus. As _Macrosporium Cheiranthi_, Pr., often is found in company with _Cladosporium herbarum_, that is also open to suspicion.

We have adduced in the foregoing pages a few instances which will serve to ill.u.s.trate the polymorphism of fungi. Some of these it will be observed are accepted as beyond doubt, occurring as they do in intimate relationship with each other. Others are considered as scarcely so well established, but probable, although developed sometimes on different species of plants. Finally, some are regarded as. .h.i.therto not satisfactorily proved, or, it may be, only suspicious.

In this latter group, however much probability may be in their favour, it can hardly be deemed philosophical to accept them on such slender evidence as in some cases alone is afforded. It would not have been difficult to have extended the latter group considerably by the addition of instances enumerated by various mycologists in their works without any explanation of the data upon which their conclusions have been founded. In fact, altogether this chapter must be accepted as ill.u.s.trative and suggestive, but by no means as exhaustive.

[A] De Bary, in "Quarterly German Magazine" (1872), p. 197.

[B] The method pursued by Messrs. Berkeley and Hoffmann of surrounding the drop of fluid, in which a definite number of spores or yeast globules had been placed, with a pellicle of air, into which the germinating threads might pa.s.s and fructify, is perhaps the most satisfactory that has been adopted, though it requires nice manipulation. If carefully managed, the result is irrefragable, though doubts have been cast, without any reason, on their observations.

[C] De Bary, "Uber die Brandpilze" (Berlin, 1853), pl. iv. figs. 3, 4, 5.

[D] A. de Bary, on Mildew and Fermentation, in "Quarterly German Magazine," vol. ii. 1872.

[E] Berkeley, "Introd. Crypt. Bot." p. 78, fig. 20.

[F] See also Berkeley, in "Trans. Hort. Soc. London," vol. ix. p.

68.

[G] Berkeley, in "Ann. Nat. Hist." (June, 1838), No. 116.

[H] "Grevillea," vol. i. p. 176.

[I] Tulasne, "On Certain Fungicolous Sphaeriae," in "Ann. des Sci.

Nat." 4^me ser. xiii. (1860), p. 5.

[J] "A Currant Twig, and Something on it," in "Gardener's Chronicle,"

January 28, 1871.

[K] Figs. 104 to 106 by permission from the "Gardener's Chronicle."

[L] Berkeley and Broome, in "Annals of Natural History" (1866), No.

1177, pl. v. fig. 36; Cooke, "Handbook," ii. p. 866.

[M] Cooke, "Handbook," ii. p. 853, No. 2549; specimens in Cooke's "Fungi Britannici Exsiccati," No. 270.

[N] Berk. and Br. "Ann. Nat. Hist." (1865), No. 1096.

[O] "Ann. Nat. Hist." (1871), No. 1332, pl. xx. fig. 23.

[P] Ibid. No. 1333, pl. xxi. fig. 24.

[Q] Tulasne, "Selecta Fungorum Carpologia," ii. p. 269, pl. 29.

[R] Cooke, "Handbook," ii. p. 878; Tulasne, "Carpologia," ii. p. 120, plate 14.

[S] Tulasne, "Selecta Fung. Carp.," ii. plate 16.

[T] Corda, "Icones Fungorum," vol. iii. fig. 91.

[U] Corda, "Icones," vol. i. fig. 25.

[V] Berk. and Br. "Ann. Nat. Hist." No. 415.

[W] Currey, in "Philosoph. Trans. Roy. Soc." (1857), pl. 25.

[X] Tulasne, "On the Reproductive Apparatus of Fungi," in "Comptes Rendus" (1852), p. 841; and Tulasne, "Selecta Fungorum Carpologia," vol. iii.

[Y] "Monatsbericht der Koniglichen Preuss, Acad. der Wissenschaften au Berlin," Jan. 1865; Summary, in "Journ. Roy. Hort. Soc., London," vol. i. n.s. p. 107.

[Z] We have before us an _aecidium_ on leaves of _Berberis vulgaris_, collected at Berne by Shuttleworth in 1833. It is named by him _aecidium graveolens_, and differs in the following particulars from _aecidium berberidis_. The peridia are scattered as in _ae.

Epilobii_, and not collected in cl.u.s.ters. They are not so much elongated. The cells are larger, and the orange spores nearly twice the diameter. There is a decided, strong, but unpleasant odour in the fresh plant; hence the name. The above figures (figs. 107, 108) of the cells and spores of both species are drawn by camera lucida to the same scale--380 diameters.

[a] Freiherrn von Hohenbuhel-Heufler, in "Oesterr. Botan.

Zeitschrift," No. 3, 1870.

[b] f.u.c.kel, "Symbolae Mycologicae" (1869), p. 49.

[c] Almost simultaneously with De Bary, the late Professor Oersted inst.i.tuted experiments, from which the same results ensued, as to _aecidium berberidis_ and _Puccinia graminis_. See "Journ.

Hort. Soc. Lond." new ser. i., p. 85.

[d] "Oversigt over det Kon. Danske Videns. Selskabs" (1866), p. 185, t. 3, 4; (1867,) p. 208, t. 3, 4; "Resume du Bulletin de la Soc. Roy. Danoise des Sciences" (1866), p. 15; (1867), p. 38; "Botanische Zeitung" (1867), p. 104; "Quekett Microscopical Club Journal," vol. ii. p. 260.

[e] This is _Podisoma foliicola_, B. and Br., or, as proposed in "Journ. Quekett Club," ii. p. 267, _Sarcostroma Berkeleyi_, C.

[f] Tulasne, "Selecta Fungorum Carpologia," iii. p. 6, pl. i. figs.

19-31.

[g] Cramer's "Papilio Exotic" (1782), fig. 267.

[h] Cooke, "Handbook," p. 548, No. 1639.

[i] Ibid. p. 556, No. 1666.