13 



POLYPLECTRON. 



POLYSTICHUM. 



Campanularia tolubilii. 



(Johnston, A Uittory of the British Zoophytet ; Milne-Edwards, A 

 Monograph of rituh Fossil Corah ; Landsborough, Popular History 

 of SritiiA Zoophyte*; Adams, Baikie, and Ban-on, Manual of Natural 

 flittory for Traveller!; articles on Zoophytology in Quarterly Journal 

 of Microscopical Science.) 



POLYPLECTRON. [PAVONIDA] 



POLYPODIA'CE-iE are one of the chief divisions of the natural 

 order of Ferns. [FiLicus.] They constitute the highest form of 

 Acrogenous or Cryptogamic vegetation, and are regarded as approach- 

 ing more nearly to Cycadaceous Qmynosperms than to any other part 

 of the vegetable kingdom now in existence. 



They are usually herbaceous plants, with a permanent stem, which 

 remains buried and rooting beneath the soil, or creeps over the stems 

 of trees, or forms a scarcely moveable point of growth, round which 

 new leaves are annually produced in a circle ; or it rises into the air in 

 the form of a simple stem, bearing a tuft of leaves at its apex, and 

 sometimes attaining the height of 50 or 60 feet. [AcROQENS.] 



The stems seem always to produce roots in great quantities from 

 their surface, even when elevated in the air; such roots are more 

 especially met with near and under the ground, where they form a 

 stratum of some thickness, acting both as feeding-organs and as an 

 external protection ; on all Tree-Fcrns they appear upon the stem at 

 least in the form of tubercles j and in Cibotium Eillardieri they cover 

 over the whole surface from the top to the bottom with a dense layer 

 several inches deep. 



The surface of tree-fern stems may be taken to represent that of 

 the order in general. It is always marked with scars of considerable 



size, having either a lozenge form or that of an irregular oval, and 

 bearing within their area evident traces of the fracture of woody 

 plates which passed from the stem into the leaves. 



These scars lengthen as the stem increases in age, till the lozenge or 

 oval form is entirely destroyed ; the scars then become separated to 

 considerable distances, and extended into long and often irregular and 

 indefinite spaces separated by deep furrows. Hence it happens that 

 the appearance of the upper and lower end of the same tree-fern 

 stem is so dissimilar, that they would not be supposed to belong to 

 even the same species. Below the scars, or interposed among them, 

 are found openings down into the interior of the stem, filled with 

 pulverulent matter, and of unknown use. They appear to be of the 

 same nature as the apertures into the superficial cells of Sphagnum, or 

 more especially as the perforations in the rhizoma of Nymphcea. 



Although tree-ferns are unknown in any countries except those 

 having either a damp tropical climate, or at least an equable mild 

 temperature and humid atmosphere, yet the common ferns of this 

 country, whose stems, vulgarly called roots, are formed under ground, 

 exhibit the same kind of organisation as that just described, only in a 

 less conspicuous manner. It does not therefore follow that the remains 

 of tree-ferns found in this country in a fossil state prove Great Britain 

 to have had formerly a tropical climate, especially as the number of 

 such remains hitherto met with has been extremely small ; the utmost 

 value that can be assigned to their evidence is that of probability. In 

 those tropical lands where the tree-fern acquires its full size, as for 

 example Brazil, the Philippines, Pitcairn's Island, &c., it becomes one 

 of the most majestic and graceful objects, having an enormous plume 

 of the most delicate and verdant foliage at the extremity of a lofty 

 flexible stem, which sways beneath the gentlest breeze. 



POLYPODIUM, a genus of Ferns, the type of the natural order 

 Polypodiaceas. The species of this genus are known by the thecse 

 being in clusters on the back of the frond, and by their opening trans- 

 versely ; the ring is usually vertical and incomplete. This is the case 

 with Attosurus and Woodsia. Polypodium is distinguished by the sori 

 being circular and naked, and the margin of the frond is flat, not 

 reflexed. Several species are found in Great Britain. 



P. vulgare, Common Polypody, has the fronds deeply pinnatifid; 

 the lobes linear-oblong, somewhat serrated, all parallel, upper ones 

 gradually smaller. This plant is very common in every part of Great 

 Britain, delighting in shady banks, walls, and old trees. It may be 

 easily cultivated in a Ward's case, amidst the smoke of our most popu- 

 lous cities. It is subject to a great many varieties. These have been 

 beautifully illustrated in Mr. Henry Bradbury's process of ' Nature 

 Printing." ' The Ferns of Great Britain and Ireland,' executed by 

 this process, and edited by Dr. Lindley and Mr. Moore, is one of the 

 most useful works that the student of ferns can consult. 



P. Phegopteris has' pinnate fronds, with the lowest pair of pinmo 

 turned downwards and forwards ; the rest are turned upwards. It 

 loves damp places, near the spray of waterfalls. 



P. Dryoj)teri> has the fronds ternate and glabrous. It inhabits shady 

 mountainous places. 



P. calcarewn has triangular subternate fronds, which are glandular- 

 mealy ; the lower branches are pinnate. It is found on broken 

 limestone ground. 



(Babington, Manual of British Botany.) 



POLYPO'GON (from iro\ii, and iruyuv, a beard), a genus of Grasses 

 belonging to the tribe Agrostidece. It has scarious nearly equal glumes, 

 each furnished with a long seta from just below the emarginate summit. 

 The pallso are shorter than the glumes, the outer ones usually curved 

 from below the summit. 



P. Mowpdiensis has the setae more than twice as long as the rather 

 obtuse glumes. It has a fibrous root, a stem from a foot to a foot and 

 a half high, a dense-lobed silky panicle often two inches long. The 

 glumes are linear and hairy. It is a very beautiful grass, and is a 

 native of Great Britain in salt marshes. It is the ' A\anr(Kovpos (Fox- 

 Tail) of Theophrastus, 'Hist. Plant.,' 7, 17. 



P. littoralis has its setro equalling the acute glumes. The root is 

 somewhat creeping, the stem about a foot high, the panicle close lobed 

 and purplish. The glumes are linear lanceolate. It is a British species 

 and is found in muddy salt marshes. 



(Babington, Manual of British Botany.) 



POLYPORUS. [DRY-ROT.] 



POLYPTERUS, a genus of Fishes belonging to the family Clnpeidce. 

 The sides of the upper jaw are immoveable ; the head is covered with 

 sharpened bony plates ; the body with strong scales ; it has one gill 

 ray ; a number of separate fins on the back ; the teeth like a rasp, 

 with long ones in front ; the stomach large ; a double air-bladder, with 

 large lobes, the left one opening freely into the gullet. There are two 

 species, one found in the Nile, the other in the rivers of Senegal. 

 These fish are interesting as forming the only living representatives of 

 a large family now extinct. They belong to the large division of 

 extinct fish called Sauroid, on account of their resemblance to the 

 Lizard tribes. [FlSH.] 



POLYSTICHUM, a genus of Plants belonging to the natural order 

 of Fit ices, the sub-order Polypodiacece, and the tribe Aspidece. The 

 indusium is circular, attached by the centre ; the veins are distinct 

 after leaving the midrib. There are three British species : 



P. Lonchitis, with rigid simply pinnate fronds. Found iu alpine rocks. 



