146 G. T. HARRIS ON THE 



of the comparatively small amount of level surface. Sucli 

 as do occur are principally made by farmers for watering cattle 

 on the farms. They are quite small, often dry, and when full 

 so frequently disturbed by cattle that no vegetation has a chance 

 of developing. Quite often, however, on the commons, small 

 pools will be formed in depressions of the land, but these have 

 been ignored when filling in the records for this column, as their 

 Desmid flora has nearly always been derived from bogs situated 

 at a higher level, from which the water has been derived. Good 

 roadside ditches also are conspicuously absent from the district, 

 as the drainage of the land surface is too effective for any standing 

 or slow-running water. Hence it is not surprising that this 

 column of the Census List makes but a poor contribution. One 

 notable feature, however, is connected with an examination of 

 such pools as do exist in the district, this is the occurrence of 

 what may be termed Closteria pools. These pools are densely 

 populated with both species and individuals of the genus Clos- 

 terium. On Dartmoor I met with the same feature in one pool, 

 which was almost exclusively populated by various species 

 of Closterium. In the present district a very notable example 

 occurred, which was an extremely small pond without any 

 macrophytic vegetation, but prolific in Closteria, fifteen species 

 being collected from it, all in profusion, but Closterium angustatum 

 being the dominant species. On a "spread" one-inch cover- 

 glass nearly 200 individuals of this species were counted : 

 very few Desmids of other genera were present, but Oscillatoria 

 princeps Vauch. was abundant in the pond. In East Devon, 

 Closterium Malinvernianum seems restricted to ponds, and 

 is rarely found even in them. Cosmarium Corhula has only 

 been found in one small hill pond, but there it occurred in 

 abundance. 



Although it has no connection with the present paper, it may 

 be of interest to mention a Closterium habitat that appears 

 somewhat unusual. The species concerned is Closterium moni- 

 liferum Ehrenb., a species by no means common in Devonshire, 

 and one that is more or less confined to small pools and ditches. 

 In the present instance, however, it occurred in the swift water 

 of the Teign Eiver at Fingle Bridge, Some alder trees growing 

 on the banks of the river had had their roots exposed by the 

 bank having been washed away, and the fine rootlets were 



