144 G. T. HARRIS ON THE 



total number of species, varieties and forms collected from 

 Woodbury Common is 367. 



Harcombe Bog. — This small bog is caused by springs that 

 break out at the junction of the Keuper Marls with the overlying 

 Greensand and Cretaceous beds. It is of no great extent and 

 quite inconsiderable depth, the whole being little more than a 

 boggy hill-side. It is situated on the eastern slope of one of the 

 long parallel ridges that traverse East Devon from north to 

 south, and is nearly on the 500-feet contour line. Its interest 

 arises from the fact that its drainage water is derived from 

 the super-incumbent Cretaceous beds, so that the bog may be 

 regarded almost as much a Cretaceous as a Triassic habitat ; 

 probably an important point, however, being that the water 

 is filtered by passing through the Grreensand beds before it reaches 

 the bog at the junction with the Marls. Notwithstanding its 

 meagre area and semi-calciphilous conditions, the Desmid 

 flora is quite equal in number of species and varieties to a second- 

 rate Dartmoor bog, its census list being about 113 species and 

 varieties. One notable feature in connection with it is the total 

 absence of any member of the genus Mesotaenium, in this respect 

 difiering markedly from the Woodbury Common bogs, which are 

 particularly rich in them. A few individuals of the common 

 Arihrodesmus Incus represent the genus Arthrodesmus. There 

 is also a remarkable absence of Micrasterias denticulata. Pure 

 gatherings were often made of Closterium Lunula and Euastrum 

 crassum, and the alga Eremosphaera viridis was often present 

 in prodigious quantities. 



Beacon Hill. — This bog is similar in physical conditions 

 to the one at Harcombe. Like that it exists where the springs 

 break out at the junction of the Greensand beds with the Keuper 

 Marls. It is also at about the same altitude. It is, however, 

 of rather greater extent, and in places probably a foot in depth, 

 owing to a considerable growth of Sphagnum, principally S. 

 acutifolium and S. cymbi folium, with several varieties. At 

 one spot a small fount of water forces itself to the surface and 

 flows down the hill-side, the swampy area around the spring 

 being richly covered with various dicotylous hydrophytes. 

 No Desmids occur around the spring, these being replaced by 

 a luxuriant growth of Diatoms. It is probable that at this spot 

 the water is richer in silica derived from the Greensand beds 



