Fungi: Their Nature and Uses

by M. C. Cooke

Fig. 108.—Cells and pseudospores of Æcidium graveolens.

Montagne has, however, described a Puccinia berberidis on leaves of Berberis glauca from Chili, which grows in company with Æcidium berberidis. This at first sight seems to contradict the above conclusions; but the Æcidium 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 Æcidium 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 Æcidia? This is the conclusion to which many have arrived, and, taking advantage of certain presumptions, have, we fear, rashly associated many such forms together without substantial evidence. On the leaves of the primrose we have commonly a species of Æcidium, 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 cacaliæ, Unger, Uredo cacaliæ, Unger, and Æcidium cacaliæ, Thumen, are considered by Heufler[a] to form one cycle. Numerous others are given by Fuckel,[] 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 Æcidium, with its constant companion, spermogonia—distinct cysts, that is, from which a quantity of minute bodies ooze out, often in the form of a tendril, the function of which is imperfectly known at present, but which from analogy we regard as a form of fruit, though it is just possible that they may be rather of the nature of spermatozoids. The Æcidia 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. 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 Æcidium, 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 Œrsted, 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 Rœstelia.[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-glasses. 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 Rœstelia appeared, and were developed. “This trial of spores,” says Œrsted, “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 Rœstelia 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 Rœstelia. 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 instituted similar experiments upon other hosts, with the spores of Podisoma, and from thence he concluded that Rœstelia 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 Rœstelia 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 Rœstelia 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 Rœstelia 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 Rœstelia 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 substituted that of Torrubia.[f] These curious fungi partake more or less of a clavate form, and are parasitic on insects. The pupæ 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 pupæ, 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,[] is said by Tulasne to be a condition of Sphærostilbe, and it is intimated that other productions of a similar character bear like relations to other sphæriaceous 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 quantity 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, circumstances 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, glassy 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 circumstances, 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 analogy render it so extremely probable that such is the case, apart from the fact of both forms springing from the same mass 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 assumption until further researches enable us to record the assumption 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. glaucum 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 identity, 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 association—for the evidence does not proceed further—was recorded by us, in which a dark-coloured species of Penicillium was closely associated with what we now believe to be a species of Macrosporium—but then designated a Sporidesmium—and a minute Sphæria growing in succession on damp wall-paper. Association is all that the facts warrant us in calling it.

We cannot forbear alluding to one of the species of Sphæria to which Tulasne[m] attributes a variety of forms of fruit, and we do so here because we think that a circumstance so extraordinary should be confirmed before it is accepted as absolutely true. This refers to the common Sphæria found on herbaceous plants, known as Sphæria (Pleospora) herbarum. First of all the very common mould called Cladosporium herbarum is constituted 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.