Alternation of Generations in Fungi

Abstract

I AM sure that the Rev. M. J. Berkeley will exonerate me from any deliberate intention to misrepresent him; nor do I think that there is, after all, much difference of opinion between us regarding the present subject, unless, perhaps, that I am more sceptical. I alluded to the paper cited by him from the “Journal of the Horticultural Society,” on propagation of bunt spores, and not to his communications on the hop or vine mildew. I was under the impression that he regarded the “four consecutive forms of reproductive cells in the bunt” as an instance of alternation of generations. On reference to the original paper, I find that he did not go so far then as to indicate four consecutive forms of reproductive cells; but that Tulasne followed on his track in 1854, and in 1857 Mr. Berkeley seemed to have accepted the results of Tulasne's observations, since, in his “Introduction,” he gives figures at page 318, in the description of which the following phrases occur:—“spores of the second order,” “spores of the third order,” “spores of the fourth order.” Here are the “four consecutive forms of reproductive cells” to which I alluded. At page 321 he writes concerning the bunt:—“The spores, however, are not immediate means of propagation; they are, in fact, only a sort of prothallus, from which the mycelium grows, producing at the tips, or on lateral branchlets, bodies of various forms, which are themselves capable of germination, and immediately reproduce the species.” The real issue between us seems to lie in the phrase, “alternation of generations.” If the bunt spores, on germination, produce fusiform bodies, which, after conjugation, produce short cylindrical spores, and thus intermediate reproductive cells unlike the parent cell come between that and the ultimate reproduction of the species, I am induced to call it an “alternation of generations.” It would be waste of time to discuss phrases, or I might take exception to the application of this phrase to the Erysiphei. The conidia and pycnidia of the hop mildew may be developed without sporangial conceptacles, and the parasite reproduced without sporangial fruit, but I cannot recognise alternation of generations in the reproduction of a species by means of conidia, stylospores, or sporidia, or by one of these alone. If such may be construed into an alternation of generations, it must be by permitting greater elasticity to the phrase. Conidia germinating and producing pycnidia, the stylospores of the pycnidia germinating and producing sporangial conceptacles, containing the sporidia which, upon germination, will produce the mycelium and conidia again, returning to the original form after two or three consecutive departures from it, appears to me a perfect type of alternation of generations. I fully admit that “if it is once established that a Puccinia produces an AEcidium, or an AEcidium a Puccinia, we should have a clear case, especially when the third form reverts to the first again.” Without the slightest desire to “depreciate the labours of Oersted and De Bary,” I cannot admit that they have established facts until their observations are confirmed, especially when there is an evident possibility of their having been deceived. I shall have no hesitation in accepting the facts when they are confirmed by independent and equally trustworthy observers, although I may be unable to account for some of the phenomena. At present I must confess that I am not so sanguine as Mr. Berkeley appears to be.