SELECTION. 9 



sisting, in the rapid portions, of bed rock, or at 

 best of only gravel and sand, which is periodi- 

 cally shifted by floods, and would be infallibly 

 swept down towards the sea if it were not for 

 the presence of huge boulders, between which 

 this gravel and sand settles down. Of course, 

 in a very heavy flood even large boulders get 

 washed down. In such rivers the average weight 

 of the trout is much smaller than in the south 

 country chalk streams, but where they are fairly 

 preserved the deficiency in average size is in a 

 degree compensated by the number. Larvas 

 which do not require weeds, but live among the 

 stones in fast stickles, are plentiful in rivers of 

 this class, while these insects are comparatively 

 rare in the clear streams of Hampshire and 

 Wiltshire. Hence the scarcity, or, in many 

 cases, absence, of such flies as the March 

 .Brown (Ecdynrus venosus) or the Stone Fly 

 (Perla cephalotes) from the Test, Kennet, and 

 other streams of like character. 



In classifying the weeds which are of real classification 



. " . t . .... of weeds. 



advantage to a river, and in which the 

 Crustaceans, Molluscae, Caddis, and larvae of 

 Ephemeridae, which are so essential a portion 

 of the natural food of chalk stream trout and 

 grayling, are more or less abundant, the most 

 important is that usually called by anglers 

 "Celery" {Apium inundatum). The name 



