Bogs and swamps 425 



B. Algal Associations of Bogs and Swamps. 



All the algal associations of bogs and swamps are mixed associations with 

 a less marked periodicity than in ponds, pools or lakes. They differ much 

 in character according to geological formations, local conditions (such as 

 prevalence of iron salts), altitude, etc. 



The commonest type of bog in temperate areas is the Sphagnum-bog, 

 although species of Hypnum play an important part in upland districts. 

 An average mixed association consists of various species of the Zygne- 

 macese in small quantity, certain desmids, the larger species being mostly of 

 the ubiquitous type, many diatoms, a few representatives of the Protococcales, 

 certain of the Blue-green Algae and sometimes one or two members of the 

 Peridiniese. Of the Zygnemacese, a few species of Zygnema and Mougeotia 

 are not infrequently met with. The most conspicuous desmids are Closterium 

 Lumda, Gl. turgidum, Cl. didymotocum, Cl. striolatum, Cl. juncidum, Cl. 

 gracile, Peniuin margaritaceum, P. spirostriolatum, Euastrum crassum, E. 

 ampullaceum, E. Didelta, E. pectinatum, Micrasterias denticulata, M. rotatci, 

 M. papillifera, M. truncata, Xanthidium armatum, Cosmarium tetr<tophthal- 

 mum, C. margaritiferum, C. Cucurbita, Staurastrmn hirsutum, St. muricatum, 

 St. Reinschii, St. brachiatum, Tetmemorus granulatus, T. Lvvis, Hyalotheca 

 dissiliens, Oymnozyga monilifonnis and many others. The diatoms are 

 especially represented by the larger species of Navicida (N. nobilis, N. major, 

 N. viridis, N. Iridis and others) and various species of Eunotia (E. Arcus, 

 E. majus, E. tetraodon, etc.). Stauroneis Plicenicenteron is very frequent and 

 Vanheurckia rlioinboides var. saxonica is often present in great abundance, 

 sometimes to the comparative exclusion of other types. Of the Protococcales, 

 Oocystis solitaria and Eretnosph&ra viridis are the most noteworthy, the 

 latter sometimes occurring in abundance among some of the larger desmids. 

 The only representative of the Heterokontse of any importance is Chlorobotrys 

 regtdaris, which may occur in considerable quantity. A number of Blue- 

 green Algee habitually occur in Sphagnam-\)0gs, of which may be mentioned 

 Stigonema ocellatum, Hapalosiphon Jtibernicus, C ylindrospermum stagnate, 

 several species of Anabiena, Synechococcus major and Chroococcus turgidus. 

 Glenodinium uliginosum, one of the Peridiniete, is also a common organism 

 amongst submerged Sphagnum, and there is evidence to show that it is 

 profoundly influenced by temperature (consult fig. 267 ; and G. S. W., '09 A). 



Cedergren ('13) has suggested that there are two decided subassociations 

 in a Sphagtmm-bog, a Sphagnetum desmidiosum characterized by the abun- 

 dance of desmids and a Sphagnetum naviculosum characterized by the 

 dominance of the larger species of naviculoid diatoms. These suggested 

 subassociations scarcely hold good, however, since the larger desmids and 



