426 



Ecology 



naviculoid diatoms so frequently occur together in abundance, evidently 

 thriving under the same conditions. 



In some of the more spongy Sphagnum-bogs Utricidaria minor is abun- 

 dant 1 and this at once adds to the richness of the alga-flora. It harbours 

 amongst its leaves more desmids and a greater variety of them than almost 

 any other aquatic macrophyte. Also, if the bogs are on the older geological 

 formations they have a much richer and more varied desmid-flora. 



Altitude has a decided effect upon the Algre of a Sphagnum-bog. In 

 north temperate latitudes the desmid-flora changes considerably with the 



PERIODICITY Of GUENODINIUM UUGINOSUM 

 IN SPHAGNUM- BOG , SUTTON PARK , W ARWIC KS. 



Fig. 267. Periodicity of Glenodinium ulifjinnfuim. The upper curve represents the water- 

 temperatures from October, 1906 to December, 1908. The lower black line represents by 

 its varying width the relative abundance of Glenodinium uliginomm at different seasons of 

 the year. 



altitude, additional species, such as Micrasterias oscitans, M. Jemteri, Cos- 

 marium Ralfsii, C. coslatum, and many others, becoming increasingly frequent 

 with increase in altitude up to several thousand feet. In the northern 

 hemisphere increase in latitude has a marked effect on the desmid-flora, 

 many arctic types making their appearance, amongst which may be mentioned 

 Xanthidium grcenlandicum, Euastrmn tetralobum, Staurastrum acarides, St. 

 subspheericum, St. rhabdophorum, Cosmarium spetsbergense, C. pericy nmtium 



1 The author has seen the deep bogs on Cocket Moss, West Yorkshire, on Thursley Common, 

 Surrey, and in parts of Achill Island, Mayo, a sheet of yellow with the flowers of Utriculnria 

 minor. Such bogs always contain a great abundance of desmids, but the number and character 

 of the species depend largely upon the nature of the geological formation. 



