309 



straight lines do not exceed the 500th of an inch in diameter. Dr. Brewster 

 also observed the remarkable fact, that each particle has a regular axis of 

 double refraction. In the straw and chaff of Wheat, Barley, Oats, and Rye, 

 he noticed analogous phenomena ; but the particles were arranged in a differ- 

 ent manner, and displaj^ed figures of singular beauty. From these data the 

 doctor concludes that the crystalline portions of silex and other earths, which 

 are found in vegetable tissues, are not foreign substances of accidental occur- 

 rence, but are integral parts of the plant itself, and probably perform some im- 

 portant function in the process of vegetable life. Grevill. Fl. Edinens. 214. 

 Example. Equisetum. 



CCLXIV. FILICES. The Fern Tribe. 



Filices, Juss. Gen. 14. (1789) ; Swartz Synops. Filicum (1306) ;' Willd. Sp. PI. vol. 5. (1910) ; 

 R. Brown, Prodr. 145. (1810) ; Agardh Aph. 115. (1822) ; Kaulfuss Enum. (1824) ; Sprang. 

 Syst. Veg. vol. 4. (1827) ; Hooker and Grevillc lcones Filicum (1827-1829.) 



Diagnosis. Flowerless plants, with their sporules either enclosed in thecae 

 arising from the back or margin of the leaves, or naked upon the back of de- 

 formed leaves. Vernation circinate. 



Anomalies. In Gphioglossere the vernation is straight. 



Essential Chabacter. — Leafy plants, producing' a rhizoma, which creeps below or upon 

 the surface of the earth, or rises into the air like the trunk of a tree ; this trunk consists of a 

 hollow cylinder, of equal diameter at both ends, containing - a loose cellular substance which 

 often disappears ; it is coated by a hard, cellular, fibrous rind, which is much thicker next the 

 root than at the apex, and is composed of the united bases of the leaves. Leaves (or fronds) 

 coiled up in vernation, with annular ducts in the vascular tissue of their petiole, either simple 

 or divided in various degrees, traversed by dichotomous veins of equal thickness, which are 

 composed of elongated cellular tissue, with occasional ducts; cuticle frequently with stomata. 

 Reproductive Organs consisting of thecce or semitransparent cases arising' from the veins upon 

 the under surface of the leaves or from their margin. Thecce either pedicellate, with the stalk 

 passing round them in the form of an elastic ring - , or sessile and destitute, of such a ring ; 

 either springing from beneath the cuticle, which they then force up in the form of a mem- 

 brane (or indusium), or from the actual surface of the leaves. Sporules usually triangular, 

 arranged without order within these thecre. Sometimes the leaves are contracted about the 

 thecae, so as to assume the appearance of forming a part of the reproductive organs, and some 

 limes the place of theca is supplied by the depauperated'lobes ol the leaves. 



Affinities. These, which are by far the most gigantic of the cellular 

 class, sometimes having trunks 40 feet high, approach the nearest to the Vas- 

 cular class by Cycadece, which may be considered to have much affinity with 

 them, on account of the imperfect degree in which their vascular system is de- 

 veloped, their pinnate leaves with a gyrate vernation, and their naked ovules 

 borne upon the margin of contracted leaves, as the thecae of Ferns are upon 

 the fronds of Osmunda. Their affinity with Equisetum, to which they were 

 formerly joined, consists more in their want of flowers, and in the presence of 

 annular ducts, than in any similarity of habit. Lycopodiaceee are readily 

 known by their axillary thecae dehiscing by two regular valves. Marsileaceoe 

 are so very different, that it is difficult to find points of comparison between 

 them. 



M. Bory de St. Vincent elevates Ferns to the rank of a class intermediate 

 between Monocotyledons and Acotyledons ; but at the same time he attaches 

 no importance to the descriptions of those writers who, having seen the germi- 

 nation of the sporules, have attempted to prove an identity between them and 

 Monocotyledons in that respect. He justly observes, that the irregular unila- 

 teral scale which has been seen to sprout forth upon the first commencement of 

 their growth is extremely different from the cotyledon of Monocotyledons, 



