POLYTiENIUM. 



[ 526 



POLYTRICHUM. 



and six. In some of the species a kind of 

 rind is formed subsequently, by a growth 

 from the base of the joints analogous to that 

 which occurs in Batrachospermum and 

 Callithamnion. The fructification consists 

 of — 1. ceramidia, attached to the sides of 

 branches, containing numerous pear-shaped 

 spores; 2. tetraspores, on distinct plants, 

 formed in the swollen central cell of distorted 

 branches (fig. 603) ; and 3. antheridia, elon- 



Fig. 603. 



Polysiphonia nigrescens. 



Distorted ramuli containing imbedded tetraspores. 



Magnified 50 diameters. 



gated whitish sacs, collected in great num- 

 bers at the summits of the branches, accom- 

 panied by a dichotomous hair, and some- 

 times prolonged into a hair-like process at 

 the summit. Nageli described the sperma- 

 tozoids as consisting of a spiral filament. 

 Thuret disagrees with this, and states that 

 they are merely hyahne globules, about 

 1-5000" in diameter. The British species 

 are placed in two subgenera : Oligosiphonia, 

 where there are but four or rarely five peri- 

 pheral cells, and Polysiphonia, where there 

 are six or more. Twenty-six species are de- 

 scribed, many of which are common. 



BiBL. Harvey, Brit. Mar. Alg. p. 82. pi. 

 12 A ; Thuret, Ann. des Sc. nat. 3 ser. xvi. 

 p. 16. pi. 6 ; Nageli, Zeitschr.f. wiss.Botan. 

 Heft 3 and 4 (1846). p. 207. pi. 6 & 7. 



POLYTiENIUM, Desv. — A genus of 

 Taenitideai (Polypodseous Ferns). Exotic. 



POLYTHALAMIA, See Foramini- 



FERA. 



POLYTOMA, Ehr.— A genus of Infuso- 

 ria, of the family Monadina (Hydromorina). 



P. uvella (PI. 24. fig. 69, undergoing di- 

 vision), the only species, is oblong or oval, 

 obtuse at the ends, colourless, furnished with 

 tw^o flagelliform filaments; it has no cara- 

 pace. Aquatic; length 1-2200 to 1-960"; 

 size of body when the division is nearly 

 complete, 1-400". 



BiBL. Ehrenberg, Infus. p. 24. 



POLYTRICHACE^.— Atribe of Mnioi- 

 dese (operculate Mosses of usually Acrocar- 

 pous habit). 



I. Catharinea. Calyptra narrowly 

 hood-sliaped, subscabrous at the apex, ra- 

 ther hairy within. Peristome simple, com- 

 posed of thirty-two teeth, arising from a 

 narrow, cellular, basilar membrane, ligulate, 

 membranous, white, vdth many percurrent, 

 reddish, inarticulate filaments, somewhat 

 incurved, scarcely hygroscopic, firm. Colu- 

 mella dilated at the apex into a drum-like 

 epiphragm. Capsule equal. Inflorescence 

 monoecious or dioecious. 



II. PoLYTRiCHUM. Calyptra dimidiate, 

 but appearing campanulate on account of a 

 quantity of very close hairs descending from 

 it as a long villous coat ; otherwise resem- 

 bling the preceding genus. 



POLYTRICHUM, Dill.— A genus of Po- 

 lytrichaceous Mosses, variously defined by 

 different authors. In the British Flora, it 



Fig. 604. 



i 



Polytrichum commune. 



Plants in fruit. 

 One-half natural size. 



