14 81. FLUVIALES. 



Native. Lacustral. The rise at once from 3 to G 

 counties, in the estimate, seems considerable ; but the 

 likeliliood also appears great that an easily overlooked 

 aquatic plant may occur in other counties intennediate 

 between, or adjacent to, those for which it has been re- 

 corded. As yet, however, it has been found only in the 

 two covmties above named as the southern and northern 

 limits, with the intermediate one of Hertford. 



1123. POTAIVIOGETOX ZOSTER^FOLIUS, Sckum. 



Area * [2] 345**8;,. [10] ^ * * * 15. 



South limit in Essex, Warwick. [Dorset ?] 



Noi-th limit in Forfar. 



Estimate of provinces 6. Estimate of counties 12. 



Latitude 51 — 57. Germanic (?) type of distribution. 



Agi'aiian region. Inferagi'arian — Midagrarian zones. 



Descends to the coast level, in Thames. 



Ascends to 100 yards, more or less, in England. 



Range of mean annual temperatui'e 49 — 47. 



Native. Lacustral. Very sparsely distributed in Bri- 

 tain, according to the recorded localities. Specimens are 

 in my herbarium from Essex (no collector's name on the 

 label), Cambridge (Mr. C. C. Babington), Warwick (IMr. 

 Thomas Kii-k), Stafford (Rev. R. C. Douglas), Leicester 

 (Rev. A. Bloxam), and Forfar (Prof. Balfom-). Besides 

 these comities it has been reported to grow in York (ex- 

 tinct?), Derby, Nottingham, within 16 miles of Poole 

 (Salter Cat.), and at Henfield, Sussex CNVinch, in N. B. G.); 

 the province of the Channel being scarcely admissible on 

 the two latter records, until fmlher confii'mation. As- 

 cends almost into the superagrarian zone. 



