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The last work of importance, in which microscopic characters were ignored, was the Enumeratio critica Lichenum Europaeum by Schaerer[122], a veteran lichenologist, who rather sadly realized at the end the limitations of that work, as he asks the reader to accept it “such as it is.” Many years previously, Eschweiler[123] in his Systema and Fée[124] in his account of Cryptogams on Officinal Bark, had given particular attention to the internal structure as well as to the outward form of the lichen fructification. Fée, more especially, had described and figured a large number of spores; but neither writer had done more than suggest their value as a guide in the determination of genera and species.

It was an Italian botanist, Giuseppe de Notaris[125], a Professor in Florence, who took up the work where Fée had left it. His comparative studies of both vegetative and reproductive organs convinced him of the great importance of spore characters in classification, the spore being, as he rightly decided, the highest and ultimate product of the lichen plant. In his microscopic examination of the various recognized genera, he found that while, in some genera, the spores conformed to one distinct type, in others their diversities in form, septation or colour gave a decisive reason for the establishment of new genera, while minor differences in size, etc. of the spores proved to be of great value in distinguishing species. The spore standard thus marks a new departure in lichenology. De Notaris published the results of his researches in a fragment of a projected larger work that was never completed. Though his views were overlooked for a time, they were at length fully recognized and further elaborated by Massalongo[126] in Italy, by Norman[127] in Norway, by Koerber[128] in Germany and by Mudd[129] in our own country. Massalongo had drawn up the scheme of a great Scolia Lichenographica, but like de Notaris, he was only able to publish a part. After twelve years of ill-health, in which he struggled to continue his work, he died at the early age of 36.

Lindsay[130], Mudd and Leighton[131] were at this time devoting great attention to British lichens. Lauder Lindsay’s Popular History of British Lichens, with its coloured plates and its descriptive and economic account of these plants has enabled many to acquire a wide knowledge of the group. Mudd’s Manual, a more complete and extremely valuable contribution to the subject, followed entirely on the lines of Massalongo’s work. From his large experience in the examination of lichens he came to the conclusion that: “Of all organs furnished by a given group of plants, none offer so many real, constant and physiological characters as the spores of lichens, for the formation of a simple and natural classification.”

Meanwhile, a contemporary writer, William Nylander, was rising into fame. He was born at Uleaborg in Finland[132] in 1822 and became interested in lichens very early in his career. His first post was the professorship of botany at Helsingfors; but in 1863 he gave up his chair and removed to Paris where he remained, except for short absences, until his death. One of his excursions brought him to London in 1857 to examine Hooker’s herbarium. He devoted his whole life to the study of lichens, and from 1852, the date of his first lichen publication, which is an account of the lichens of Helsingfors, to the end of his life he poured out a constant succession of books or papers, most of them in Latin. One of his earliest works was an Essay on Classification[133] which he elaborated later, but which in its main features he never altered. He relied, in his system, on the structure and form of thallus, gonidia and fructifications, more especially on those of the spermogonia (pycnidia), but he rejected ascospore characters except so far as they were of use in the diagnosis of species. He failed by being too isolated and by his unwillingness to recognize results obtained by other workers. In 1866 he had discovered the staining reactions of potash and hypochlorite of lime on certain thalli, and though these are at times unreliable owing to growth conditions, etc., they have generally been of real service. Nylander, however, never admitted any criticism of his methods; his opinions once stated were never revised. He rejected absolutely the theory of the dual nature of lichens propounded by Schwendener without seriously examining the question, and regarded as personal enemies those who dared to differ from him. The last years of his life were passed in complete solitude. He died in March 1899.

Owing to the very inadequate powers of magnification at the service of scientific workers, the study of lichens as of other plants was for long restricted to the collecting, examining and classifying of specimens according to their macroscopic characters; the microscopic details observed were isolated and unreliable except to some extent for spore characters. Special interest is therefore attached to the various schemes of classification, as each new one proposed reflects to a large extent the condition of scientific knowledge of the time, and generally marks an advance. It was the improvement of the microscope from a scientific toy to an instrument of research that opened up new fields of observation and gave a new impetus to the study of a group of plants that had proved a puzzle from the earliest times.

Tulasne was one of the pioneers in microscopic botany. He made a methodical study of a large series of lichens[134] and traced their development, so far as he was able, from the spore onwards. He gave special attention to the form and function of spermogonia and spermatia, and his work is enriched by beautiful figures of microscopic detail. Lauder Lindsay[135] also published an elaborate treatise on spermogonia, on their occurrence in the lichen kingdom and on their form and structure. The paper embodies the results of wide microscopic research and is a mine of information regarding these bodies.

Much interesting work was contributed at this time by Itzigsohn[136], Speerschneider[137], Sachs[138], Thwaites[139], and others. They devoted their researches to some particular aspect of lichen development and their several contributions are discussed elsewhere in this work.

Schwendener[140] followed with a systematic study of the minute anatomy of many of the larger lichen genera. His work is extremely important in itself and still more so as it gradually revealed to him the composite character of the thallus.

Several important monographs date from this period: Leighton[141] reviewed all the British “Angiocarpous” lichens with special reference to their “sporidia” though without treating these as of generic value. He followed up this monograph by two others, on the Graphideae[142] and the Umbilicarieae[143], and Mudd[144] published a careful study of the British Cladoniae. On the Continent Th. Fries[145] issued a revision of Stereocaulon and Pilophoron and other writers contributed work on smaller groups.