62 EQUISETACEvE. [Acrogems. 



growing and combining, until a considerable cellular mass is formed ; then this mode 

 of development censes, and a young bud is created, which springs up in the form of the 

 stem of tbe Equifietum, at once completely organised, with its air-cells, its central 

 cavity, and ita sheaths, the first of winch is formed before the elongation of the stem, 

 out of the original cellular matter. 



Horsetails are found in ditches and rivers in most parts of the world, within and 

 wiili. >ut tin- tropics. 



None are of importance in a medical point of view; they are said to be slightly 

 astringent and .stimulating, and have even been recommended as diuretics and 

 emmenagognee ; they are, however, not now employed. In economical purposes they 

 are found to be useful for polishing furniture and household utensils — a property 

 which i» due t.) the presence of a great quantity of silex in their cuticle. According to 

 the observations of John of Berlin, they contain full thirteen per cent, of siliceous 

 earth. The ashes have been found by chemists to contain half their weight of silica. 

 The quantity of silex contained in the cuticle of Equisetum hyemale is so great, that 

 Sivrighl succeeded in removing the vegetable- matter and retaining the form. On sub- 

 jecting a portion of the cuticle of Equisetum hyemale to the analysis of polarised light 

 under a high magnifying power, Brewster detected a beautiful arrangement of the 

 siliceous particles, which are distributed in two lines parallel to the axis of the stem, 

 and extending over the whole surface. The greater number of the particles form 

 simple Btraight lines, but the rest are grouped into oval forms, connected together like 

 the jewels of a iieeklaee, by a chain of particles forming a sort of curvilinear quadrangle, 

 rows of ova4 combinations being arranged in pairs. Many of those particles 

 which form the straight lines do not exceed the 500th of an inch in diameter. Brew- 

 ster 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 different manner, and 

 displayed figures of singular beauty. From these data it is concluded that the crystal- 

 line 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 function in the process of vegetable life. A very 

 large quantity of starch is found during whiter in the rhizomes ; in whose cells, during 

 the month of October, the particles may be seen in active motion, passing up one side, 

 and retreating by the other, much iu the same way as in Chara. This I have often 

 noticed in Equisetum fluviatile. 



GENUS. 

 Equisetum, L. 



Numbers. Gen. 1. Sp. 10 



CharacecB. 



Position. Marchantiacea;. — Equisetace.e. 



Gnetacece. 



The first discovery of the analogy between the development of the spore in germi- 

 nation in the Ferns and Equisetacese, is due to M. G. Thuret, who saw the spores of 

 the latter produce a cellular pro-embryo somewhat like that 

 of the Ferns, and in this were developed antheridis of 

 analogous structure, emitting cellules containing many spiral 

 filaments. This announcement was confirmed by M. Milde, 

 whose observations extended over some months, during which 

 time no "ovule" was produced, but he saw what appeared 

 to be the rudiment of one. Dr. Mettenius states that he has 

 met with decaying "ovules" precisely like those of the Ferns, 

 upon the pro-embryo of one Equisetum ; and thus the evidence 

 is completed, so far as the occurrence of the two kinds of 

 organs is concerned. — Henfrey. 



M. Thuret, in his last work (Rcclierckes, &c), describes the 



Pig. XUV. antherids as growing at the end of the lobes of the prothal- 



lium. They are larger than in Ferns. The terminal cells of 



the lobes separate to allow the autherozoids to escape, and remain on the lobes like 



minute coronets. The antherozoids themselves resemble those of Ferns. 



1 \ LIV.— Antherid of Euuisetuni, magnified: with three antherozoids, still more magnified, 

 seen at the side— after Thunt. 



