TIIALLOPIITTES. By reason of their cellular structure the thallophytes were poor subjects for preservation, while from their mieroseopic size they would be exceedingly difficult to detect even when preserved. Their comparative rarity as fossils is then to he expected, and such of their traces as are known are for the most part nothing more than casts or markings. Time schizophytes. representing the agencies of disintegration and decay. were undoubtedly present at the very dawn of life. but their early existence is predicated upon theoretical grounds.
The fungi are also of comparatively little im portance in fossil botany. They are represented by thallus and mycelium fragments, or by the effects produced presumably by these growths in the tissues of higher plants, notably in those of the Carboniferous period, and there is every reason to believe that they were among the earliest floral elements of the earth. A com plete enumeration of all the known fossils which have been classed as fungi has been made by Alloysius Meschinelli, in his Fungoruat Fos silia»t thallium, published at Venice in 180s, in which are listed and described about 400 species, included in about 70 genera. The lichens are almost unknown as fossils. Those found are apparently referable to living genera; they con sist mostly of flakes on fragments of lignite or are inclosed in amber, and none is known from horizons below the Tertiary. The alga' are rep
resented by the earliest known definite traces of vegetable organisms, even if all the prob lematic casts and tracings which have been referred to these plants are eliminated. .Many of these latter to which generic names have been given may be considered as mere mechanical markings, such as are made by ripples, sun or frost cracks. etc., or by the tracks or burrows of marine animals. In the former class may be included the genera Eophyton, Vexillum, Gonio phycus. etc.. and in the latter. Scolithus, Phytop sis, Eilobites, etc. Nevertheless, if all these un certain forms are disregarded. a large number of fossil species are known. which are apparently referable to the larger marine alga.• and are included in the genera Buthotrephis. Lierophy cus, Noniatophyeus, Lithothamnion, Cliondrites, etc., which occur in rocks of all ages from the Cambrian upward.
The diatoms are the most abundant as well as the most perfectly preserved of all the thallo phytes, their siliceous tests generally retaining perfectly their original characters. They occur in abundance from the Cretaceous period up ward, often forming extensive beds of 'tripoli' or diatomaceous earth. such as those of Bilin in Bohemia a ml Richmond in Virginia. (S(4• Di