so 81. FLUVIALES. 



1131. POTAMOGETON EUFESCENS, ScllVad. 



Area 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17. 



South limit in Cornwall, Sussex, Kent. 



North limit in Caithness, Aberdeen, Ai-gyle. 



Estimate of provinces 17. Estimate of counties 70. 



Latitude 50—59. British tj-pe of distribution. 



Agi-arian region. Inferagrarian — Superagrarian zones. 



Descends to the coast level, in the Peninsula. 



Ascends to 100 or 200 yards, in England. 



Range of mean annual temperature 51 — 46. 



Native. Lacustral. Less liable to be mistaken, than 

 are several of the other species ; though probably some 

 of the published localities truly belong to the fluitant 

 form before mentioned, as intermediate between P. hete- 

 rophyllus and P. oblongus. I have received examples of 

 it also under the names of lucens (Essex and Lancaster; 

 B. S. London) and prselongus. I have seen no example 

 from the North Highland province; but Dr. George 

 Johnston informed me that he had seen specimens which 

 were gathered in Caithness by Mr. Tyacke. If P. fluitans 

 of the Flora of Northumberland and Diu-ham has been 

 correctly referred to P. rufescens, the altitude above in- 

 dicated may probably be doubled ; but it is more likely 

 to be P. oblongus. 



1132. POTAMOGETON NATANS, Linn. 



Area general. 



South limit in Cornwall, Isle of "Wight, Kent. 



North Umit in Shetland, Orkney, Hebrides. 



