Möller’s experiments with ascospores and pycnidiospores were primarily undertaken to prove that the lichen hyphae were purely fungal and parasitic on the algae. A series of cultures were made by Hedlund[730] in order to demonstrate that the pycnidiospores were asexual reproductive bodies; they were grown in association with the lichen alga and their germination was followed up to the subsequent formation of a lichen thallus.
d. Variation in Pycnidia. On the thallus of Catillaria denigrata (Biatorina synothea) Hedlund found that there were constantly present two types of pycnidia: the one with short slightly bent spores 4-8 µ × 1·5 µ, the other with much longer bent spores 10-20 µ × 1·5 µ; there were numerous transition forms between the two kinds of spores. Germination took place by the prolongation of the spore; the hypha produced became septate and branches were soon formed. Hedlund found that frequently germination had already begun in the spores expelled from the spermogonium. In newly formed thalline areolae it was possible to trace back the mycelium to innumerable germinating spores of both types, long and short.
Lindsay had recorded more than one form of spermogonium on the same lichen thallus, the spermatia varying considerably in size; but he was most probably dealing with the mixed growth of more than one species. The observations of Möller and Hedlund on this point are more exact, but the limits of variation would very well include the two forms found by Möller in Calicium trachelinum; and in the different pycnidia of Catillaria denigrata Hedlund not only observed transition stages between the two kinds of spores, but the longer pycnidiospores, as he himself allows, indicated the elongation prior to germination: there is no good evidence of more than one form in any species.
F. Pycnidia with Macrospores
Tulasne[731] records the presence on the lichen thallus of “pycnidia” as well as of “spermogonia”; the former producing stylospores, larger bodies than spermatia, occasionally septate and containing oil-drops or guttulae. These spores are pyriform or ovoid in shape and are always borne at the tips of simple sporophores. He compared the pycnidia with the fungus genera Cytospora, Septoria, etc. As a rule they occur on lichens with a poorly developed thallus, on some species of Lecanora, Lecanactis, Calicium, Porina, in the family Strigulaceae and in Peltigera.
There is no morphological difference between pycnidia and spermogonia except that the spermatia of the latter are narrower; but the difference is so slight that, as Steiner has pointed out, these organs found on Lecanora piniperda, L. Sambuci and L. effusa have been described at one time as containing microconidia (spermatia), at another macroconidia (stylospores). He also regards as macrospores those of the pycnidia of Calicium trachelinum which Möller was able to germinate so successfully, and all the more so as they were brownish in colour, true microspores or spermatia being colourless.
Müller[732] has recorded some observations on the pycnidia and stylospores of the Strigulaceae, a family of tropical lichens inhabiting the leaves of the higher plants. On the thallus of Strigula elegans var. tremula from Madagascar and from India, he found pycnidia with stylospores of abnormal dimensions measuring 18-26 µ in length and 3 µ in width, and with 1 to 7 cross septa. In Strigula complanata var. genuina the stylospores were 2-8-septate and varied from 7-65 µ, in length, some of the spores being thus ten times longer than others, while the width remained the same. Müller considers that in these cases the stylospore has already grown to a septate hypha while in the pycnidium. As in the pycnidiospores, described later by Hedlund, the spores had germinated by increase in length followed by septation.
The spermogonia of Strigula, which are exactly similar to the pycnidia in size and structure, produce spermatia, measuring about 3 µ × 2 µ, and it is suggested by Müller that the stylospores may represent merely an advanced stage of development of these spermatia. Both organs were constantly associated on the same thallus; but whereas the spermogonia were abundant on the younger part of the thallus at the periphery, they were almost entirely replaced by pycnidia on the older portions near the centre, only a very few spermogonia (presumably younger pycnidial stages) being found in that region.
Lindsay[733] has described a great many different lichen pycnidia, but in many instances he must have been dealing with species of the “Fungi imperfecti” that were growing in association with the scattered granules of crustaceous lichens. There are many fungi—Discomycetes and Pyrenomycetes—parasitic on lichen thalli, and he has, in some cases, undoubtedly been describing their secondary pycnidial form of fruit, which indeed may appear far more frequently than the more perfect ascigerous form, and might easily be mistaken for the pycnidial fructification of the lichen.