312 



able fact, that each particle has a re^jjular 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 different manner, and 

 displayed 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 occurrence, but are 

 integral parts of the plant itself, and probably perform some important func- 

 tion in the process of vegetable life. Grevill. Fl. Edinetis. 214. 

 Example. Equisetum. 



CCLXIV. FILICES. The Fern Tribe. 



FiLicES, Juss. Gen. 14. (1789); Swartz Synops. Filicilm (1806); Tf^illd. Sp. PI. vol. 5. 

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

 (1824); Spreng. Syst. Veg. vol. 4. (1827); Hooker and Greville Icones 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 deformed leaves. Vernation circinate. 



Anomalies. In Ophioglossese the vernation is straight, 



.Essential Characteb 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 con- 

 sists of a hollow cylinder, of equal diameter at both ends, containing' a loose cellular sub- 

 stance which often disappears ; it is coated by a hard, cellular, fil)rous rind, which is much 

 thicker next the root than at the apex, and is composed of the united bases of the leaves. , 

 Leaves {ot 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 celhilar tissue, with occasional ducts ; cuticle 

 frequently with stomata. Reproductive organs consisting of theccB or semi transparent cases 

 arising from the veins upon the under surface of the leaves or from their margin. Theca 

 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 membrane (or indusium), or from the actual surface of the leaves. 

 Sporules ustially triangular, arranged -wathout order within these thecw. Sometimes the 

 leaves -are contracted about the theca-, so as to assume the appearance of forming a part of 

 the reproductive organs, and sometimes the place of theca is supplied by the depauperated 

 lobes of 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 

 Vascular cjass by Cycadeae, which may be considered to have much affinity 

 with them, on account of the imperfect degree in which their vascular system 

 is developed, 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 Osn"iunda. Their affinity with Equisetum, to which they 

 were formerly joined, consists more in their want of flowers, and in the pre- 

 sence of annular ducts, than in any similarity of habit. Lycopodiaceae are 

 readily known by their axillary thecit dehiscing by two regular valves. Mar- 

 sileaceae 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 ger- 

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

 and Monocotyledons in that respect. He justly observes, that the irregular 

 unilateral scale which has been seen to sprout forth upon the first com- 



