. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . two decided subassociationsin a Sphagtmm-bog, a Sphagnetum desmidiosum characterized by the abun-dance of desmids and a Sphagnetum naviculosum characterized by thedominance of the larger species of naviculoid diatoms. These suggestedsubassociations scarcely hold good, however, since the larger desmids and 426 Ecology naviculoid diatoms so frequently occur together in abundance, evidentlythriving under the same conditions. In some of the more
. Algæ. Vol. I. Myxophyceæ, Peridinieæ, Bacillarieæ, Chlorophyceæ, together with a brief summary of the occurrence and distribution of freshwat4er Algæ . two decided subassociationsin a Sphagtmm-bog, a Sphagnetum desmidiosum characterized by the abun-dance of desmids and a Sphagnetum naviculosum characterized by thedominance of the larger species of naviculoid diatoms. These suggestedsubassociations scarcely hold good, however, since the larger desmids and 426 Ecology naviculoid diatoms so frequently occur together in abundance, evidentlythriving under the same conditions. In some of the more spongy Sphagnum-bogs Utricidaria minor is abun-dant1 and this at once adds to the richness of the alga-flora. It harboursamongst its leaves more desmids and a greater variety of them than almostany other aquatic macrophyte. Also, if the bogs are on the older geologicalformations they have a much richer and more varied desmid-flora. Altitude has a decided effect upon the Algre of a Sphagnum-bog. Innorth temperate latitudes the desmid-flora changes considerably with the PERIODICITY Of GUENODINIUM UUGINOSUMIN SPHAGNUM- BOG , SUTTON PARK , W ARWIC Fig. 267. Periodicity of Glenodinium ulifjinnfuim. The upper curve represents the water-temperatures from October, 1906 to December, 1908. The lower black line represents byits varying width the relative abundance of Glenodinium uliginomm at different seasons ofthe year. altitude, additional species, such as Micrasterias oscitans, M. Jemteri, Cos-marium Ralfsii, C. coslatum, and many others, becoming increasingly frequentwith increase in altitude up to several thousand feet. In the northernhemisphere increase in latitude has a marked effect on the desmid-flora,many arctic types making their appearance, amongst which may be mentionedXanthidium grcenlandicum, Euastrmn tetralobum, Staurastrum acarides, , St. rhabdophorum, Cosmarium spetsbergense, C. pericynmtium 1 The author has seen the deep bogs on Cocket Moss, W
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