917 



Kfyz Crta&trg of 2Satattg. 



[POMA. 



toraentose branches, cordate hirfcellous 

 '.eaves, and umbels bearing ratlier large ! 

 green flowers. The calyx is five-cleft, the 

 corolla bell-shaped, and the corona consists 

 of twenty-five leaves. The fruit is un- 

 known. [B. S.] j 



POLYSTEMOXOTTS. Having a much 

 larger number of stamens than petals. 



POLYSTICHOI. One of the principal 

 genera into which the old genus Aspidium j 

 is broken up by modern pteridologists. It 

 is separated from the rest by its free veins, 

 globose sori, and peltate indusia, no other 

 ferns having these peculiarities combined. 

 The fronds are in general rigid and coria- 

 ceous,with the margins mucronato-serrate ; 

 and hence they have a distinct aspect, 

 which serves to distinguish them almost 

 as clearly as their technical characters. 

 They are included in Aspidium by those 

 who do not admit the genera founded on 

 diversity of venation. The species are 

 numerous and widely dispersed, some few 

 occurring in Britain. [T. M.] 



POLYTJEXIA. A genus of urnbell if ers, 

 having an oval and smooth fruit, each half 

 of which has five obscure ribs, with two 

 oil-cells in each furrow, and six on the 

 line of junction. P. NuttaUii is the only 

 species, a native of Arkansas in the 

 United States ; it is an herb with yellow 

 flowers. The name was given in allusion 

 to the numerous oil receptacles of the 

 fruit. [G. D.] 



POLYTOMOUS. Pinnate, but without 

 having the divisions articulated with the 

 common petiole. 



POLYTRIC OFFICINAL. (Fr.) Asple- 

 nium Trichomanes. 



POLYTRICHEI. A natural order of 

 acrocarpous mosses, characterised by the 

 mouth of the capsule being closed by a flat 

 membrane formed by the top of the colu- 

 mella and confluent with the tips of the 

 teeth, and a calyptrarous-h with dependent 

 silky hairs which were originally a sort of 

 paraphyses, though distinct from the true 

 attendants on the archegonia. The order ; 

 is remarkable for containing some of the 

 finest genera among mosses, as Dawsonia, ' 

 Lyellia, &c. : the former an Australian 

 genus extending to New Zealand, with an 

 oblique capsule, and an indefinite number 

 of concentric teeth in the peristome, which 

 are either quite free or partly connected 

 with the top of the columella; and the ! 

 latter a Xepalese .genus with a similarly 

 shaped capsule whose mouth is entirely j 

 closed with a membrane, from which a cen- j 

 tral orbicular portion separates, together i 

 with the columella which contracts within j 

 the capsule. Potytrichum, the typical genus, j 

 contains many common British species, i 

 known at once from all other mosses by J 

 their peculiar habit and veW.Atrichum un- 

 dulatum, which is common in grassy shady 

 places, is distinguished from the rest by I 

 the absence of hairs on the veil. [M. J. B.] 



POLYTRICHUM. A fine genus of aero- ! 



carpous mosses with a peculiar rigid habit, 

 a veil rough with dependent hairs, and the 

 mouth of the capsule closed with a flat mem- 

 brane continued from the tips of the teeth. 

 The capsule is angular, and furnished with 

 a little apophysis below. The spore-sac is 

 sometimes separated from the columella as 

 well as from the walls of the capsule. The 

 species are numerous, and occur in all parts 

 of the world. In P. dendroides the stem is 

 highly developed, and shows scalariform 

 markings in some of its tissue, accom- 

 panied by lighter-coloured cells which coh- 



Polytriclium commune. 



tain starch-grains. P. commune, though at- 

 taining its largest size in marshy heaths, is 

 not confined to them ; it is' sometimes 

 formed into brushes or plaited into mats 

 for the feet. [M. J. B.] 



POLYSENA. A genus of Liliacece from 

 the Cape of Good Hope, allied to Massonia, 

 but differing in the funnel-shaped perianth 

 with the stamens inserted in the tube (not 

 a prolongation of it upwards), and by the 

 perianth being circumscissilely deciduous ; 

 seeds one or two in each of the three cells ; 

 leaves lanceolate, somewhat fleshy ; flowers 

 racemed, pale violet or rose. [J. T. S.j 



POLYZONE. A South-west Australian 

 genus of ChamcelauciacecB, consisting of 

 shrubs with whorled branches, needle- 

 shaped three-angled leaves, and flowers 

 in sessile terminal heads surrounded by a 

 many-leaved coloured involucre. This with 

 Genetyllis and Hedaroma are now referred 

 to Barwinia. [R. H.] 



POMACE^E. (Appleworts.) A natural 

 order of calycifloral dicotyledons belonging 

 to Lindley's rosal alliance of perigynous 

 Exogens. The plants are often considered 

 as a suborder of Rosacea. They are trees or 

 shrubs with alternate stipulate leaves, and 

 solitary or cymose regular flowers ; calyx 

 superior, five-toothed, the odd segment su- 

 perior ; petals five, the odd one inferior ; 

 stamens numerous ; disk lining tube of ca- 

 lyx ; ovaries one to five ; ovules anatropal ; 

 styles one to five. Fruit a one to five- 

 celled pome ; seeds exalbuminous. Com- 



