81. FLUVIALES. 21 



Estimate of provinces 18. Estimate of counties 82. 



Latitude 50 — 61. British type of distribution. 



Agi-arian region. Inferagi'arian — Superagrarian zones. 



Descends to the coast level, in the Peninsula. 



Ascends to 350 yards, in East Highlands. 



Range of mean annual temperatui-e 52 — 43. 



Native. Lacustral. This is generally believed to be 

 the commonest species of its genus in Britain, and the 

 fact may be so. But as P. plantagineus and P. oblongus 

 have been always confused, more or less, with the present 

 species, some degree of uncertainty will attach to the dis- 

 tribution, as above drawn out from the records of its 

 locahties. My herbarium has no specimen from any 

 county more northerly than Kincardine. ■^-^■^ ^- 7^'^^ 



1133. POTAMOGETON (oblongus^ Viv. 



Area 1 2 3 * 5 * 7 8 9 10 * 12 * 14 15 16 17 18. 



South limit in Devon, Isle of Wight, ? 



North limit in Orkney, Hebrides. 



Estimate of provinces 18. Estimate of counties 80. 



Latitude 50 — 60. British type of distribution. 



A. A. regions. Inferagrarian — Inferarctic zones. 



Descends to the coast level, in the Peninsula. 



Ascends to 500 yards, or thereabouts, in East Highlands. 



Range of mean annual temperature 51 — 41. 



Native. Lacustral, Uliginal. The localities of this 

 species are much confused with those of tliree other spe- 

 cies, — natans, heteroj)hyllus, rufescens. When growing 

 out of water, in swampy spots on our heaths and moors, 

 or even in still and shallow waters, it has closely the form 

 and appearance of P. natans, and has doubtless often been 

 so named. The fluitant form, before mentioned under 



