POLYPODIES. 



[ 623 ] 



POLYSTOMELLA. 



** Indusium absent. 



POLYPODIES. Sori on the back of the 

 lobes, round or rarely oblong, not more 

 than twice as long as broad. 



GBAMMITIDES. Sori on the back of the 

 lobes, more than twice as long as broad, 

 usually linear. 



ACBOSTICHES. Sori spread over the 

 under surface or rarely both surfaces of the 

 frond, not confined to the veins. 



POLYPODIES. A family of Polypo- 

 diaceous Ferns; contains the single genus 

 Poll/ podium. 



POLYPODIUM, Linn. A genus of 

 Ferns with naked sori, of which there are 

 several indigenous representatives, P. vul- 

 gare, the Oak-Fern, being- one of our com- 

 monest species. Exceedingly well adapted | 

 for examination of the structure of the sori 

 and sporanges in this family. 



POLYPOR'EI. A family of Hymeno- 

 mvcetous Fungi, characterized by bearing 

 baddiospores lining tubes, pores, or pits, 

 on the underside of a stalked or sessile 

 j> ileus, or fleshy cap or disk. The basidio- 

 spores are seen by horizontal sections from 

 the undersurface of the pileus. (See BA- 

 SIDIOSPORES and HYMEXOMYCETES.) 



BIBL. Berk. Fruct. of Fungi, Ann. N. H. 

 i. 81 ; LeYeille", Ann. Sc. N. 2. viii. 324. 



POLYSAC'CUM, D. Cd. A genus of 

 Trichogastres (Gasteromycetous Fungi), 

 having a common peridium filled with 

 peridiola ; the spores mixed with threads. 

 One species only occurs, and Tery rarely in 

 this country. Abroad they grow on exposed 

 sand. One of the species has been used in 

 dyeing. -P. crassipes, p. 349, fig. 269. 

 "BIBL. Fr. Syst. Myc. iii. 54; Berk. 

 Outl. 304; Sow. t. 425; Cooke, Handb. 

 375. 



POLYSEL'MIS, Duj. A doubtful genus 

 of Infusoria, of the family Euglenia. 



Char. Oblong or variable in form, with 

 several anterior flagelliforrn filaments, and a 

 single red eye-spot. 



Probably the zoospore of a Confervoid 

 Alga. 



P. viridis (PI. 31. fig. 68) resembles a 

 Euylena of an oblong form with the ends 

 rounded ; one of the filaments is longer than 

 the three or four others which surround its 

 base. Freshwater ; length 1-650". 

 BIBL. Dujardin, Infus. 370. 

 POL YSIPHO'NIA, Grev. An extensive 

 genus of Rhodonieleee (Florideous Algae) or 

 Red sea-weed.s, with cylindrical, more or less 



Fig. 598. 



articulated fronds, the joints consisting of a 

 circle of longitudinally arranged cells sur- 

 rounding a central cell, like the wood- 

 bundles of a young Dicotyledonous stem 

 surrounding the pith, so that the transverse 

 section presents the appearance of a rosette. 

 The number of peripheral cells varies among 

 the 300 different species of this genus, from 

 four to twenty-five ; the British forms 

 mostly have four 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 BATRA- 

 CHOSPERMUM and CALLITHAMNION. The 

 fructification consists of: 1. ceramidia, urn- 

 shaped or ovate, attached to the sides of 

 branches, containing nume- 

 rous pear-shaped spores at 

 the base ; 2. tetraspores on 

 distinct plants, formed in the 

 swollen central cell of dis- 

 torted branches (fig. 598) ; 

 these are gonidia and develop 

 a thallus ; and 3. antheridia, 

 elongated whitish sacs, col- 

 lected in great numbers at 

 the summits of the branches, 

 accompanied by a dichoto- 

 rnous .hair, and sometimes 

 prolonged into a hair-like 

 process at the summit. Nageli 

 describes the spermatozoids 

 as consisting of a spiral fila- 

 ment. Thuret states that 

 they are merely hyaline glo- 

 bules, about 1-5000" in dia- 

 meter, without active motion. 

 The British speciesareplaced 

 in two subgenera Oligosi- 

 phonia, where there are but 

 four or rarely five peripheral 

 cells, and Po/y*e)?A0ma, where 

 there are six or more. 

 Twenty-six species are de- 

 scribed, many of which are common. 

 fastigiata, PL 4. fig. 20.) 



BIBL. Harvey, Mar. Alg. 82, pi. 12 A ; 

 Thuret, Ann. Sc. N. 3. xvi. 16, pi. 6 ; Nageli, 

 Zeitsch. wiss. Sot. 1846, 207, pis. 6 & 7 ; 

 Henfrey-Masters, Sot. 433. 



POLYSTOMEL 'LA, Lamk. A genus of 

 Hyaline Foraminifera. Shell free, regular, 

 equilateral, biconvex, sometimes compressed, 

 often dorsally keeled; spire embracing; 

 chambers with a single cavity, straight or 

 arched, meeting at the umbilicus and fur- 

 nished with transverse pits between the 



Magn. 50 diams. 



(-P- 



