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 BOTANY The classification and nomenclature adopted are in accordance with Cooke's British Freshwater Algae (18824) anc ^ ^is British Desmidieee (18867), exce pt that his order Zygophyceaa is divided into the two families Desmidiea? and Botrydiaceas, the desmids forming such a natural group that it is well to keep them separate. The order Coccophyceas and the family Desmidieas contain the species of most interest. Of the two species of Chlamidococcus (the old genus Protococcus}, our only record of C. nivalis is in a paper by Mr. R. B. Croft 'On the Occurrence of Red Snow in Hertfordshire.' ] This species 'was regarded by Bauer as a fungus, by Robert Brown as an alga, and by Baron Wrangel as a lichen.' 2 Mr. Croft doubted the colour of the snow being due to the alga, believing it to be caused by the pres- ence of the flagellate animalcule Euglena acus, but he sent specimens of the melted snow to three observers, including Mr. Saville Kent, and each detected the presence of Chlamidococcus. It is known, however, that snow has been coloured red and green in Spitzbergen by Euglena sanguinea and E. viridis? With regard to the other species of Chlamido- coccus, C. pluvialis, we have an interesting observation by Mr. C. W. Nunn of Hertford. The phenomenon of 'alternation of generations' exhibited by this species is well known. It is accompanied by a change in colour from red to green and back again to red. But for ten years in succession Mr. Nunn noticed the alga appearing in two tanks in his garden not ten yards apart, red in one tank and green in the other, and never changing colour. 4 The pretty Vohox globator, always an interesting object under the microscope, has been found several times at field meetings of the Hert- fordshire Natural History Society, and has frequently been exhibited at the evening meetings. The desmids are nearly all free-swimming plants living in fresh and clear water, and chiefly frequenting shallow pools and very gentle streams. The rarer Hertfordshire species are Hylacotheca mucosa, Closterium setaceum, Micrasterias furcata, and Staurastrium muricatum. The Floridea?, which are mostly marine, are represented only by our two species of Batrachospermum, B. moniliforme, a species prolific in varieties, of which we have three, and B. atrum, a very pretty species. Both frequent streams and ditches. The Diatomacea? have received more attention in the county than any of the other families of Alga?. Hassall 5 recorded twenty-four species from the neighbourhood of Cheshunt, of which one is a form of another, and two cannot now be identified. Mr. Isaac Robinson * gave a list of ninety-eight species collected in the neighbourhood of Hertford, 1 Trans. Herts Nat. Hist. Sue. vol. i. p. 170 (1881). 2 Cooke's Algee, p. 54. 8 Prof. Meyen, in Ann. and Mag. Nat. Hist. Aug. 1848. 4 'Notes on Protococcus,' Trans. Herts Nat. Hist. Soc. vol. i. p. xlv. (1882). & British Freshwater Alg* (1845). 6 ' The Diatomaceae. . .' Trans. Herts Nat. Hist. Soc. vol. iii. p. 9 (1884). 67