116 BRITISH CHAROPHYTA. 



plane non foetet, nee ab initio, quod innuere videtur 

 Micheli, sed per siccitatem saltern idq. levissime pulla 

 fuscaqu&sit. Forte ant em huic idem fuerit Equisetum 

 non /miens sub aquis repens Preston Raii Hist. Hi. 104, 

 Syn. Hi, 133, Epist. 313. 



Outside the British Isles N. mucronata is recorded 

 from Norway, Sweden, Finland, Denmark, Portugal, 

 Spain, France, Belgium, Germany, Switzerland, Austria, 

 Hungary, Italy, Boumania, Turkey and Russia; also 

 from N.W. Africa, Asia and N. America. 



A medium-sized plant 15-30 cm. high, of a darkish green 

 colour, usually rather bushy in growth, somewhat resembling* 

 in appearance a slender form of N. flexilis, but at once dis- 

 tinguishable by the frequently twice-forked branchlets and 

 the 2-celled ultimate ray, easily seen with a lens. The ultimate 

 cell of the terminal ray in the typical forms being very narrow, 

 often at its base not more than the breadth of the penulti- 

 mate cell, and tapering to a sharp point, gives the characteristic 

 mucronate outline from which the specific name was taken. 

 The var. gracillima however presents a marked variation from 

 the type. 



The antheridium is relatively small, its diameter being less 

 than the breadth of the oogonium. The lengthening of the 

 spiral cells of the oogonium as it reaches maturity is very 

 marked in this species, and the interstices between them below 

 the coronula, for the admission of the antherozoids, can be 

 readily seen. 



The scattered localities in England in which the plant has 

 been found are in a narrow band from N. Hants & W. Sussex 

 to W. Norfolk. It is singularly fugitive and seems rarely to 

 occur in the same station in two successive years. 



N. mucronata is extremely variable ; our figure is taken 

 from the rather elongated form from the River Ouse at 

 Bedford. In the British forms there is little difference 

 between the fertile and sterile whorls, so that the growth is 

 uniformly lax, but in the var. heteromorpJia Kiitz., which 

 is found in many places on the Continent, the fertile whorls 

 are small and crowded, forming more or less dense heads. 

 The var. tenuior Braun (= N. flabellata Kiitz.), is a weak 

 slender form, with a smaller oospore. N. Wahlbergiana 

 Wallm., treated as a subsp. of N. mucronata by Braun, is a 

 rare Scandinavian type with short secondary rays ; another 



