PLEA. 



[ 326 ] 



FLORIDE.E. 



rnt substance (PHORMIUM). See FIBROUS 

 STRUCTURES of Plants, and LIBER.] 



FLEA. See PULEX. 



FLINT. This is a subtranslucent variety 

 of silica, forming nodules or bands in most 

 limestones. The organisms in flint are the 

 same as those met with in the chalk or other 

 limestone of which the flint forms part, as 

 a pseudomorphic replacement of the original 

 amorphous carbonate of lime by silex, 

 generally where decomposing organic matter 

 induced the conditions of change. 



Much of the flint of the South of England 

 has been formed out of the calcareous mud, 

 crowded with small sponges, spicules, and 

 Foraminifera, which hold the same position 

 in the flint as they did in the cretaceous 

 ooze. Large sponges are often included, 

 with shells of Mollusks and Echinoderms, 

 scales of Fishes, and sporangia of Desrni- 

 diaceae, formerly recorded as distinct organ- 

 isms (Xanthidia). 



The crystallized calcite of Echinoderms 

 and some shells is not replaced by silex in 

 limestones, but remains as cavities in ex- 

 posed flint-masses. Many varieties of lime- 

 stone, viz. polyzoan limestone in France, 

 freshwater limestone in France and Turkey, 

 orbitoidal limestone in Jamaica, oolitic 

 limestone at Portland and elsewhere, are 

 converted into flint, hornstone, &c. of fine 

 or coarse grain according to the constitution 

 of the original limestone. 



"Wallich has suggested that chalk-flints 

 are due to the nearly continuous proto- 

 plasmic layer among extensive sponge- 

 growths having become silicified. 



In the examination of flint, thin sections 

 should be made by grinding and polishing ; 

 some kinds exhibit the organisms contained 

 in them best by reflected, others by trans- 

 mitted light. Some specimens, in which 

 they are abundant, will exhibit them well 

 in chips removed by a hammer. 



See AGATE and CHALK. 



BIBL. That of AGATE and CHALK ; 

 Ehrenb. Ann. N. H. 1838, ii. 162 ; Turner, 

 Phil Mag. 1833 ; Ansted,Ann. N. H. 1844, 

 xiii. 248 ; Bowerbank, ibid. 1847, xix. 240 j 

 Charlesworth, Geol.Jn. 1847, i. 29; Church, 

 Proc. Chem. Soc. 1862 ; id. Chem. News, v. 

 95, and Phil. Mag. (4) xxiii. 95 ; Sutherland, 

 Geol. Mag. ii. 220; Johnson, "Flint? 1871 ; 

 Jones, Proc. Geol. Assoc. iv. 439 ; Wallich, 

 Qu. Jn. Geol. Soc.. Feb. 1880: Sollas, -4ww. 

 N.H. 



FLORID'E^E or RHODOSPO'REyE. 

 An order of Algae. Red sea- weeds, some 



of the common species of which must be 

 familiar to every one, as the delicate feathery 

 or leaf -like plants brought away by most 

 visitors to the sea-coast ; and the red colour, 

 more or less permanent or fleeting, is a 

 pretty general characteristic of this order 

 varying however to purple, brown, and 

 mixed tints of red, green, and yellow, and 

 dirty white ; the green colour of the chloro- 

 phyll being often obscured by a red pigment, 

 phyco-erythrine. They chiefly grow in deeper 

 water than the other sea-weeds, and are met 

 with in finest and darkest colour in deep 

 tide-pools of sea-water, especially on the 

 side facing the north, where they are over- 

 hung by the larger dark-coloured Algae, and 

 thus shaded from the sun's rays. The greater 

 number do not grow more than six inches 

 high, few more than two feet. The simple.' t 

 foims are filaments composed of cylindrical 

 cells attached end to end ; they next rise 

 to a gelatinous or cartilaginous expansion, 

 composed of such filamentous structures 

 adherent in layers, and forming a com \ act 

 frond of definite shape. These are said to 

 be of filamentous structure. Others have the 

 frond composed of a number of polyg< n;;l 

 cells, evenly arranged, and with thick walla, 

 or, as some state, an intercellular substance 

 binding them all together into amass ; these 

 are technically said to be of cellular fttrm-fure. 

 Sometimes all the cells of the frond con- 

 tain colouring-matter, sometimes only those 

 of the surface, or of a shallow superficial 

 stratum. 



The general external appearance of the 

 Red Sea-weeds is very varied. Sometimes 

 the fronds are like little leafless bushes ; at 

 others they form broad laminae ; sometimes 

 the lower part is stalk-like, and the upper 

 parts spread into leaf-like lobes. In Ucles- 

 seria we have a close imitation of a regu- 

 larly formed leaf of one of the l.igher plants. 

 The leaf-like forms are either simple, lobed, 

 or exquisitely pinnate or feathered ; and the 

 Rhodosperms of warmer climates exhibit 

 most elegantly reticulated fronds. Some of 

 these plants deposit carbonate of lime in 

 their tissues in such quantity that they 

 become quite stony, so that, the vegetable 

 form alone remaining, they are commonly 

 mistaken for true corals (see CORAL). By 

 placing these corallines and mdlipores in 

 vinegar or dilute hydrochloric acid, the lime 

 is removed, and the cellular vegetable orga- 

 nization may be recognized. The tiopical 

 forms of the corallines are far more varied 

 and beautiful than our own. 



