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Love, and Power —which he maintained to constitute insuperable barriers in the development of species by natural selection alone. Mr. Wallace has admitted the difficulty in the case of the brain ; is he prepared to deny it in the case of the other two? He maintains —so far as appears at present, unanswerably
—that man cannot have been produced by the unaided power of natural selection : does not that raise a strong presumption in favour of the introduction of another agent in other cases also ? He has marked out very clearly and conclusively the limits of natural selection in the origination of species ; can he set any limits to the controlling and interfering Power which he has invoked to fill up the deficiency?
By M. C. COOKE, M.A.
I menditions or stawany speciesha
TT is now generally admitted that a great many fungi, forI merly regarded as good and distinct species, are, in reality, only conditions or stages of other forms. It has been proved beyond doubt that many species of fungi are truly polymorphic, appearing under different phases. It is, notwithstanding all this, most premature and unjustifiable to conclude, as some have done, that there are no good species at all, or that there is no certainty whatever in the study. Whilst admitting that many of our old notions have been overturned, that what at one time we hardly deemed possible has been proved to take place, we are not prepared to go the length of some, whose knowledge of the subject falls far short of their assumption. It is not very long since that one writer gravely asserted his opinion that all the British species of Æcidium, for instance, would be reduced to a single species; that, in fact, there was no sound specific distinction between them. This opinion originated probably rather in prejudice than as the result of study and investigation. Others have lumped together a host of unassociated species, without satisfactory evidence, and declared them to be only the same thing under different conditions. Hasty generalisations in this, as in other cases, produce more harm than good.
It is exceedingly difficult to trace such minute organisms as fungi, especially moulds, and to prove, without doubt, that they are conditions, the one of the other. It is easy enough to sow the spores of a certain Mucedine on paste, or potato, or any other matrix, cover them carefully, and watch the result; then, if the common Aspergillus or Penicillium makes its appearance, to some minds it is at once conclusive that the said Mucedine is only a condition of Aspergillus or Penicillium. Such a conclusion is not only rash, but mischievous, and far from the truth. There is no evidence that the Aspergillus or Penicillium originated from the spores of the Mucedine which were sown, but perhaps never germinated. When two moulds proceed apparently from the selfsame mycelium, judgment may be pronounced too hastily, for the mycelium of both may be distinct, though interlaced together; the safest conclusion being based on two forms of fruit when developed upon the same thread. Beyond this, there is always room for doubt. Hence it will be seen how difficult it is to prove dimorphism in moulds under such conditions. In many cases it is more presumption than proof. These remarks are not made with the view of discrediting the conclusions of such observers as Professor De Bary and the brothers Tulasne, but rather as a caution against assuming as fact that which is only conjecture.
Messrs. Tulasne, in their splendid work, “ Selecta Fungorum Carpologia,” have given a great number of instances of polymorphism. We have no reason to doubt that in many cases, perhaps most, they are quite correct, but even some of their conclusions require verification before they can be accepted as established fact. As an illustration of the results determined with regard to one species by these authors, we may instance the very common Sphaeria (Plæospora) herbarum. It occurs on the dead stems of herbaceous plants, on the leaves of some trees, and even sometimes on decaying Alga. On pea and bean stems it is usually plentiful. In fact, it is almost the commonest Sphæria, and easily recognised. The sporidia are, of course, contained in elongated, transparent, membranaceous asci; they are of a yellowish-brown or amber colour, ovate-oblong, and divided by numerous septa, with transverse divisions. The asci are enclosed within carbonaceous perithecia.
Equally as common, and even more so, is a mould which forms sooty or dark olive spots, or patches, on all kinds of decaying vegetable substances. This is called Cladosporium herbarum. It may be characterised as cosmopolitan, and one of the commonest, if not the commonest, of fungi. Under the microscope this mould consists of a profuse mycelium, from which arise tufts of jointed threads, mixed with elliptical or elongated spores, ultimately septate. This mould is one condition, according to M. Tulasne, of Sphæria herbarum.
Another condition of the same plant is a very pretty mould found mixed with, or parasitic upon, the Cladosporium, and known as Alternaria tenuis. This species is figured in Corda's “ Prachtflora," and consists of chains of spores resembling inverted jointed clubs. The joints are also transversely divided, as in the Sphæria sporidia.
A third form of the same species is that named by Rev. M. J. Berkeley Macrosporium sarcinula, which is developed on decaying gourds. The spores are clavate, at length somewhat rectangular, with numerous septa, constricted, and very variable, both in size and in the number of cells.
Besides these, there are certain “ distinct papillate, or bottleshaped cysts, which contain naked spores, capable of germination.” So that altogether we have five different forms of fungi, all of which are but stages or conditions of one and the same thing. It is very probable that, in addition to these, spermutia may also hereafter be discovered, or traced to some already known Coniomycetous species. From this example it will be readily understood what we mean when writing of “polymorphic fungi.”
Having thus, as it were, defined our terms, we will proceed to notice two instances of apparent polymorphism which have come before us. We say “ apparent" advisedly, because in the second instance only suspicions can be predicated. Some two or three years ago we collected a quantity of dead box-leaves, on which grew a mould named by Link Penicillium roseum. This mould has a roseate tint, and occurs in patches on the leaves; the threads are erect and branched above, bearing oblong, somewhat spindle-shaped, spores. When collected these leaves were examined, and nothing was observed or noted upon them except the Penicillium. After some time, certainly between two and three years, during which 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, and the patches of Penicillium were found to be intermixed with another mould of a higher development and far different character (Pl.LXVIII. fig.5). This mould, or rather Mucor, for it belongs to the Mucorini, 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 has been named Mucor hyalinus. 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 Mucom afterwards appeared on the same leaves, sometimes from the same patches, and from the same mycelium. The great difference in structure of the two species lies in the fructification. In Penicillium, of which the figure 4 of our plate (Pl. LXVIII.) is a good illustration, the spores are naked, and in moniliform threads, whilst in Mucor the spores are enclosed within globose membranous heads or sporangia, as shown in fig. 5. The moulds, or Mucedines, to which Penicillium belongs, are included in one of the large family of fungi termed Hyphomycetes, and the Mucors belong to another family, the Physomycetes. We entertain no doubt whatever that the Mucor, to which we have alluded as growing on box-leaves, intermixed 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 doubt 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 both forms, 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 the assumption until further researches enable us to record the assumption as fact.
In Lewis's recent “Report on Microscopic Objects found in Cholera Evacuations” (Calcutta, 1870), a similar instance of presumed dimorphism between precisely the same genera is thus recorded. “On a preparation preserved in a moist chamber on the third day a white speck was seen in 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 dew-drop 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." Here we have another example of a Mucor developed from a Penicillium, and one observation strengthens and confirms the other.
Before entering upon the details of the second apparent polymorphism, it may be as well to give some particulars of the circumstances under which the fungi appeared. It was our fortune-good fortune as far as this investigation is concerned—to have a portion of wall in our dwelling persistently damp for some months; it was close to a cistern that became leaky. The wall was papered with “marbled " paper, and varnished. At first there was for some time-perhaps inonths - nothing worthy of observation except a damp wall; decidedly