62 EQUISETACEyE. [Acrogens. 



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

 of development ceases, and a young bud is created, which springs up in the foi-m of the 

 stem of the Equisetum, at once completely organised, with its au'-cells, its central 

 ca\aty, and its sheaths, the first of which is formed before the elongation of the stem, 

 out of the original cellular matter. 



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

 without the 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 dim'etics and 

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

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

 which is due to the presence of a gi'eat quantity of silex in then' cuticle. According to 

 the observations of John of Berhn, they contain full thu-teen per cent, of siliceous 

 earth. The ashes have been found by chemists to contain half then' weight of sihca. 

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

 Si%Tight succeeded in remoAing the vegetable matter and retaining the form. On sub- 

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

 under a high magnif^-ing power, Brewster detected a beautiful arrangement of the 

 sihceous 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 straight lines, but the rest are grouped into oval forms, connected together Hke 

 the jewels of a necklace, by a chain of particles forming a sort of cxu'vilinear quadrangle, 

 these rows of oval 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 in the same way as in Chara. This I have often 

 noticed in Eqviisetum fluviatile. 



GENUS. 

 Equisetum, L. 



Numbers. Gen. 1. Sp. 10 ? 



CharacecB. 

 PosiTiox. Marchantiaceae. — Equisetace^. 



Crnetacece. 



