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 A HISTORY OF HERTFORDSHIRE thoroughly established itself in every one of our six botanical districts. In 1874 Pryor first noticed Poterium muricatum in the county, and only a single stray specimen of Bromus aruensis had then been seen in it, but by 1881 he was able to give some thirty localities for the former in the Ivel, Colne, and Lea districts, and half the number for the latter in those districts and the Cam. These and other colonists have become so perfectly naturalized that no suspicion of their exotic origin might be raised were not the history of their introduction known. The following Rubi recorded by Mr. Pryor are not included in the district lists. The districts in which they occur are indicated by the figures I 6 Idaeus, L. 2, 3, 4, 6 Plicatus, Welbe et Nees. 4, 6 Affinis, Welhe et Nees. 4, 6 Lindleianus, Lees. 4, 6 Rhamnifolius, Welbe et Nees. 3-6 Thirsoides, Wimm. 6 Ulmifolius, Schott. 1-6 Villicaulis, We'the. 3, 4 Umbrosus, Arrb. 4, 6 Macrophyllus, Weihe. 4, 6 Fusco-ater, Welhe et Nees. 4 (?) Sprengelii, Weihe. 4, 6 Leucostachys, Schleich. 26 Lejeunii, Weihe. 4, 6 Radula, Weihe. 4, 6 Rudis, Weihe. 3, 4, 6 Pallidus, Weihe. 4, 6 Rosaceus, Weihe. 6 Glandulosus, Bell. 4, 6 Praeruptorum, Boulay. 5 (?) Hystrix, Weihe. 6 Koehleri, Weihe. 2, 3, 4, 6 Pygmaeus, Weihe. 4 Scaber, Weihe. 4, 6 Humifusus, Weihe. 6 Hirtus, Waldst. et Kit. 4, 6 Guntheri, Welhe. 3, 4, 6 Bellardi, Welhe. 3 Corylifolius, Sm. 1-6 Balfourianus, Bhx. 6 Nemorosus, Blayne. z, 4, 6 Althaeifolius, Host. 6 Tuberculatus, Bab. 4, 5, 6 Diversifolius, Llndl. 4 Caesius, L. 14, 6 Pseudo-idaeus, Lej. 4, 6 CRYPTOGAMIA The cryptogamic plants have hitherto usually been divided into the two classes Acrogens and Thallogens, but Dr. M. C. Cooke 1 has shown that this classification is inappropriate in the present state of our know- ledge, and has suggested the following threefold division, which is here adopted Pteridophytes, including the Ferns and Fern-allies. Bryophytes Mosses and Hepaticae. Thallophytes Characeae, Algae, Lichens, and Fungi. In the following account of the Hertfordshire cryptogams an at- tempt is made to arrive at a census of the genera and species known to occur in the county, the names of each genus being given together with the number of its species when they are not individually enumerated. The result is as follows Genera Species Pteridophytes. Bryophytes. Thallophytes. 92 200 219 i, 06 1 Genera Species Filices. 12 . 18 Equisetaceae I 5 Lycopodiaceae. I i ' Musci. . . 61 75 . Hepaticae 3i 44 (Characeae . . 3 7 Algae . . . 63 . 252 Lichenes 21 . 67 Fungi . . .113 .735 This gives a total of 306 genera and 1,304 species of cryptogamic plants actually recorded, but this must be much under the number pre- sent. Numerous species of Ustilagineae (smut-fungi) undoubtedly occur, although not a single species has been recorded ; moulds (Hyphomy- cetes) are everywhere, but very few species are on record .; and although 1 Handbook of British Fungi, p. 3 (1895). 60