POKRIGO. 



[ 629 ] 



TOTTIOJDE^. 



PORRI'GO. SeeFAvus. 



POTAMOOY'PBIS, Brady. One of the 

 CypridfB ; valves reniform, thick, right 

 larger than left ; upper antennae with very 

 short setae ; post-abdominal rami rudimen- 

 tary. 1 British species. 



BIBL. Brady, Nat. Hist. Tr. North. $ 

 Durham, iii. 365. 



POTASH, AND ITS SALTS. 



Caustic Potash. The strength of the 

 solution may be that of the Liq. Potasste 

 of the Pharmacopoeia. But we prefer a 

 stronger solution made with 1 drachm of 

 the potassa fusa or stick-potash of the 

 shops, and 1 fluid oz. of water. The solu- 

 tion should be allowed to settle, and the 

 clear portion poured off into one of the 

 test-bottles (!NTR, p. xxvii). 



Some remarks are made upon the action 

 of potash in the INTR,, and others under 

 the heads of the tissues, &c. On treating 

 organic substances with this reagent, the 

 cystic-oxide-like crystals of the carbonate 

 (PI. 10. fig. 26) will frequently be formed. 



Chromates of Potash. The bichromate is 

 used in the preparation of the chromate of 

 lead for injection. Its crystals polarize 

 well. The neutral chromate is also some- 

 times used for preparing injections. See 



PREPARATION. 



Nitrate of potash, nitre, or saltpetre. 

 This salt is dimorphous : it usually crystal- 

 lizes in six-sided prisms with dihedral sum- 

 mits, or in other forms belonging to the 

 right-rhombic prismatic system. But some- 

 times it assumes the form of obtuse rhom- 

 bohedra, resembling those of nitrate of soda, 

 and referable to the rhombohedric system. 



The crystals exhibit very beautifully the 

 phenomena of ANALYTIC CRYSTALS. 



POTATO-FUNGUS. See BOTRYTIS. 



POT'TIA, Ehr. A genus of Pottiaceous 

 Mosses, including some of the Gymnostoma 

 and Weissice of Hedwig and others. Wilson 

 separates as Anacalyptce the species with a 

 peristome (fig. 606). 



Fig. 606. 



POTTIA'CE^E. A tribe of Pottioi 



Pottia caespitosa. 

 Fragment of peristome. 

 Magnified 50 diameters. 



Synopsis of Genera. 



Pottia. Calyptra dimidiate. Peristome 

 simple or wanting ; if present, composed of 

 lanceolate articulate teeth, simple or with a 

 longitudinal line, rugulose and somewhat 

 fleshy. 



Trichostomum. Calyptra dimidiate. Peri- 

 stome simple, sixteen teeth, each split to the 

 base into two cilia, or irregularly and there- 

 fore into more than two, erect, stiff, and 

 not twisted. 



Barbula. Calyptra dimidiate- hood - 

 shaped. Peristome simple, ciliiform ; cilia 

 thirty-two, solitary or approximated in 

 pairs on a more or less exserted basilar 

 membrane, split into two cilioles behind, 

 very long, articulate-rugulose, twisted to 

 the' left, rarely to the right, in one or several 

 spires, hygroscopic. Cells of the operculum 

 and calyptra twisted in the same way. 



Ceratodon. Calyptra dimidiate. Peri- 

 stome simple ; teeth sixteen, connate at the 

 base into a cellular membrane, split into 

 two long, nodosely articulated dark-coloured 

 arms, paler on each side, densely trabeculated 

 at the lower part. Capsule thick-skinned, 

 shining, nodding, with a somewhat nodose 

 collum; annulate. 



Weissia. Calyptra dimidiate. Peristome 

 simple or wanting ; if present, composed of 

 sixteen lanceolate or subulate, entire or 

 cribrose, equidistant teeth. 



POTTIOI'DE^E. A family of Acrocar- 

 pous operculate Mosses, but sometimes 

 Pleurocarpous by innovating branches. 

 Leaves of varied form, with a terete nerve ; 

 cells parenchymatous, hexagonal or squa- 

 rish six-sided, looser at the base, sometimes 

 very lax, more or less pellucid, often ex- 

 ceedingly transparent, large, fragile, rigid, 

 foraminate, bearing on the upper side soli- 

 tary papillae or confluent papillae (hence 

 often truncate and tuberculate at the apex), 

 placed in the middle of the cell ; cells 

 mostly full of chlorophyll, often very small 

 and thickened. Capsule erect, rarely in- 

 clined, oval, elliptic or pear-shaped oblong, 

 smooth or striate, the operculum mostly 

 conical or beaked. 



This family is divided into three tribes : 



CALYMPERACE^E. Basilar cells of the 

 leaves rigid, hyaline, often very brittle, 

 more or less ample, empty, distinctly fora- 

 minated. 



POTTIACE^E. Basilar cells of the leaves 



