PAL 



[357] 



PAL 



and was met with in the lacustrine 

 formation at Ostend, near Bacton, 

 in Norfolk. 



PAL^OTHBI'SSTJM. The name assigned 

 to a genus of fossil fishes discovered 

 in the metalliferous schists of 

 Mansfield, Thuringia, &c. This 

 genus comprises several species, as 

 the P. macrocephalum, P. magnum, 

 P. parvum, and P. ina3quilobum. 

 Hitherto this genus has been found 

 fossil only, and in strata anterior 

 to the chalk. 



PALAEOZOIC. Formerly termed pri mary . 

 The palaeozoic or primary epoch 

 comprises six periods, namely, 

 the Cambrian, the Lower Silurian, 

 the Upper Silurian, the Devonian, 

 the Carboniferous, and the Per- 

 mian. 



PA'LEA. (palea, chaff, Lat.) In bot- 

 any, a term applied to the inner 

 bracteae of grasses : the palese are 

 membranous or chaffy in texture. 



PALLA'DIFM. (from the planet Pallas.) 

 A metal of a greyish or bluish- 

 white colour, discovered by Dr. 

 "Wbllaston in 1803, in platinum. 

 It is malleable, ductile, and flexi- 

 ble, but does not possess much 

 elasticity. In hardness it sur- 

 passes all other metals, with the 

 exception of tungsten, which it 

 equals. Specific gravity 11*8. It 

 is not oxidated by the action of the 

 atmosphere. It is fusible only at 

 a very high temperature. Symbols 

 Pd. 



PA'LLEAL. (from pallium, a mantle, 

 Lat.) In conchology, the name 

 given to the mark or impression 

 observed in bivalves, formed by the 

 muscular attachment of the mantle. 



PA'LLIOBRANCHI'ATA. The same as 

 -Brachiopoda. 



PALM, (from palma, Lat.) The palms 

 constitute a natural order of mono- 

 cotyledonous, or endogenous, plants. 

 The flowers are hermaphrodite, or 

 polygamous. Perianth six- par ted, 

 persistent. Stamens inserted into 

 the base of the perianth, definite or 



indefinite. Ovary three-celled, or 

 deeply three-lobed, with an erect 

 ovule. Fruit baccate or drupaceous, 

 with fibrous flesh. Albumen car- 

 tilaginous ; embryo in a cavity at 

 a distance from the hilum. Leaves 

 terminal, large, pinnate, or flabelli- 

 form, plaited in vernation. Spadix 

 enclosed in a valved spatha. Flow- 

 ers small. 



A palm tree affords an example 

 of the mode of growth in endo- 

 genous plants. The stem of this 

 tree is usually perfectly cylindrical, 

 attains a great height, and bears 

 on its summit a tuft of leaves. It 

 is composed of an extremely dense 

 external cylindric layer of wood; 

 but the texture of the interior 

 becomes gradually softer and more 

 porous as it approaches the centre. 

 It has neither medullary rays, nor 

 central pith, nor true outward 

 bark. The first stage of its growth 

 consists in the appearance of a 

 circle of leaves, which shoot up- 

 wards from the neck of the plant, 

 and attain during the first year, a 

 certain size. The following year 

 another circle of leaves arises ; but 

 they grow from the interior of the 

 former circle, which they force 

 outwards as their vegetation ad- 

 vances, and as ligneous matter is 

 deposited within them. As soon 

 as the outer layer has become too 

 hard to yield to the pressure from 

 within, the growth of the inner 

 layers is immediately directed up- 

 wards; so that they rise in suc- 

 cession by distinct stages, always 

 proceeding from the interior; a 

 mode of development which has 

 been compared by De Candolle to 

 the drawing out of the sliding 

 tubes of a telescope. The whole 

 stem, whatever height it may 

 attain, never increases in diameter 

 after its outer layer has been con- 

 solidated. A circle of leaves 

 annually sprouts from the margin 

 of the new layer of wood ; these, 

 x x 



