A. Introductory
The term “lichen” is a word of Greek origin used by Theophrastus in his History of Plants to signify a superficial growth on the bark of olive-trees. The name was given in the early days of botanical study not to lichens, as we understand them, but to hepatics of the Marchantia type. Lichens themselves were generally described along with various other somewhat similar plants as “Muscus” (Moss) by the older writers, and more definitely as “Musco-fungus” by Morison[23]. In a botanical work published in 1700 by Tournefort[24] all the members of the vegetable kingdom then known were for the first time classified in genera, and the genus Lichen was reserved for the plants that have been so designated since that time, though Dillenius[25] in his works preferred the adjectival name Lichenoides.
A painstaking historical account of lichens up to the beginning of modern lichenology has been written by Krempelhuber[26], a German lichenologist. He has grouped the data compiled by him into a series of Periods, each one marked by some great advance in knowledge of the subject, though, as we shall see, the advance from period to period has been continuous and gradual. While following generally on the lines laid down by Krempelhuber, it will be possible to cite only the more prominent writers and it will be of much interest to British readers to note especially the work of our own botanists.
Krempelhuber’s periods are as follows:
I. From the earliest times to the end of the seventeenth century.
II. Dating from the arrangement of plants into classes called genera by Tournefort in 1694 to 1729.
III. From Micheli’s division of lichens into different orders in 1729 to 1780.
IV. The definite and reasoned establishment of lichen genera based on the structure of thallus and fruit by Weber in 1780 to 1803.
V. The arrangement of all known lichens under their respective genera by Acharius in 1803 to 1846.
VI. The recognition of spore characters in classification by De Notaris in 1846 to 1867.
A seventh period which includes modern lichenology, and which dates after the publication of Krempelhuber’s History, was ushered in by Schwendener’s announcement in 1867 of the hypothesis as to the dual nature of the lichen thallus. Schwendener’s theory gave a new impulse to the study of lichens and strongly influenced all succeeding investigations.