2-2 81. FLUVIALES. 



the head of P. heterophyllus, has certainly been occa- 

 sionally referred to that species, occasionally to the pre- 

 sent ; and perhaps it may still include the approximating 

 forms of both species, if really not a transition state be- 

 tween them. With P. rufescens the present species would 

 seem to have little likelihood of being confused ; but 

 the use of the name " fluitans " has apparently led to 

 confusion ; that name being sometimes apj)lied to exam- 

 ples of P. oblongus, sometimes held synonymous with 

 rufescens by English botanists. Perhaps actually more 

 general than P. natans, although not so recorded. 



1134. POTAMOGETON PLANTAGINEUS, DuCV. 



Area * 2 3 4 * 6 7 8 * 10 11 12 * 14 * 16. 



South limit in Hants, Kent. 



North limit in Ai'gyle (Oban), Berwick. 



Estimate of provinces 12. Estimate of counties 30. 



Latitude 50 — 57. British (?) type of distribution. 



Agrarian region. Inferagrarian — Superagrarian zones. 



Descends to the coast level, in Channel. 



Ascends to 300 yards, or upwards, in Tyne. 



Range of mean annual temperature 51 — 45. 



Native. Lacustral or Uliginal. Hitherto tliis has been 

 reported only from about twenty counties ; but as few 

 English botanists distinguish it from P. natans and P. 

 oblongus, and as the recorded counties are scattered 

 through much of Britain, many intermediate localities 

 may reasonably be expected. 



1135. ZOSTERA MARINA, &C. 



(See pages 25 — 26.) 



