STUDIES OF BRITISH FRESHWATER ALG^. 
33 
found one year and not the next, and none of the species just 
enumerated are as characteristic of the flora as Cladophora^ 
Spirogyra, etc. 
Lastly, a large number of species (in great part unicellular or simple 
colonial forms) are only found in any quantity at irregular periods, 
or are never represented by more than a few individuals. These are : — 
Vaucheria sessilis (Vauch.), D C. 
Stigeoclonium spec. 
Aphanocli(^te repens, A. Br. 
Zygnema spec.^ 
Closterium acerosum (Schrank), 
Ehrenb. 
,, parrulum. Nag. 
,, rostratum, Ehrenb. % 
,, Venus, Kiitz. % 
Cosynariuin cyclicum, Lund. 
,, granatum, Breb. 
,, renifovme (Ralfs), 
Arch. 
,, suhcucumis, Schmidle. 
,, undulatum, Corda. 
,, undulatum var. 
Wollei, West. 
Pleurotoinium Trabecula 
(Ehrenb.), Nag. 
Protoderma viride, Kiitz. 
Pediastrum tetras (Ehrb.), Ralfs. 
Characium spec. 
Scenedesmus acutus, Meyen. 
,, quadricauda 
(Turp.), Breb. 
Anhistrodesmus setigerus 
(Schrod.), West.i 
Kirchneriella lunaids (Kirchn.), 
Moeb. 
Ghlamydomonas spec. 
Volvox glohator (L.), Ehrenb.^ 
Euglena spec. 
Phacus pleuronectes, Nitzsch.^ 
Anahcena spec.^ 
Cliamce, siphon spec. 
Navicula granulata, Breb. ? 
,, major, Kiitz. 
,, molar is, Kiitz. 
Cymatopleura Solea (Breb.), 
W. Sm. 
Nitzschia sigmoidea (Ehrenb.), 
W. Sm. 
Pleu rosigma acuminatum 
(Kiitz.), Grun.i 
Amphora oralis, Kiitz. ^ 
Surirella splendida (Ehrenb.), 
Kiitz.i 
The algal flora of the pond therefore, although including a large 
number of difierent species, bears a very definite stamp, which it 
retains even during the abnormal periods to be considered below. 
The abundance of the Diatom-flora is in accord with the fact that the 
temperature of the water is on the whole rather low (cf. p. 31.) In 
view of the geological formation on which the pond is situated ^ the 
scarcity of Desmids is noteworthy ; the number of individuals present is 
generally very small, and only the three genera Closterium, Cosmarium, 
and Pleurotcenium were observed. This is no doubt due to the fact 
^ These forms are rare and of rather isolated occurrence. 
- cf. W. and G. S. West, “ A Monograph of the British Desrnidiaceae,” Yol. I. 
(1904), pp. 14, 15. Desmids “only beconie generally abundant on the older 
Palmozoic Rocks, or on rocks of an igneous or metamorphic character.” 
c 
