68 BTVOP8I8 OF BRITISH SEAWEEDS. 



Annual. Summer. Common on the shores of the British 



Island-. 



This species is subject to BOme minor variations, accord- 

 ing to the locality m which it grows. When found on 

 rocks, in exposed situations, near low-water mark, the 

 filaments are more robust, of greater length, and much 

 more branching. When growing on the stems of Lami- 

 naria digitata the filaments are much less branched, the 

 lateral branches shorter, and the ramuli remarkably squar- 

 rose, often hooked backwards. To the naked eye the ex- 

 treme states of these two varieties are sufficiently charac- 

 terized, but various intermediate forms insensibly connect 

 them. 



107. formosa (TJie beautiful Polysiphonia) • filaments exceed- 

 ingly slender and flaccid, full-red, much divided ; branches 

 subdichotomous, long, flexuous, more or less furnished with 

 scattered, spreading, alternate, subulate ramuli ; articulations 

 marked with two broad tubes, those of the main branches 

 many times (5-10 times) longer than broad, of the ramuli 

 short ; siphons four, surrounding a minute cavity ; capsules 

 urceolate, generally stalked ; tetraspores imbedded in the 

 middle part of the ramuli, Suhr. Pot. Zeit. 1831, p. 709. 

 (Atlas, PL XXV. Fig. 110.) 



Polysiphonia gracilis, Grev. 



Hab. Atlantic shores of North Britain. On rocks, near low-water 

 mark. Annual. Summer. Not uncommon. 

 P. formosa differs from P. urceolata chiefly in the much 

 greater tenuity of its filaments, and the greater propor- 

 tional length of its joints ; it agrees with that species in 

 its colour, its ramification, and the peculiar form of its 

 capsules. One appears to be a plant of bays and estuaries ; 

 the other, of the more exposed parts of the coast. 



108. pulvinata (The cushioned Polysiphonia) ; filaments rising 

 from a mass of creeping fibres, tufted and interwoven, short, 

 very slender, flexuous, sparingly and irregularly dichoto- 

 mous, more or less furnished with very patent or recurved, 

 simple ramuli ; articulations of the main branches three or 

 four times as long as broad, of the ramuli very short, four- 

 tubed ; capsules urn-shaped, stalked, Spreng. Syst. Veg. v. 4. 

 p. 350. (Atlas, PL XXV. Fig 112.) 



Polysiphonia macrocarpa, Harv. Hutchinsia pulvinata, Ag. 



* Conferva pulvinata, Roth. 

 Hab. On rocks in the sea, between tide-marks. Annual. Not 

 uncommon. 



