200 MORPHOLOGY. 



at the same results, although at the time I was unacquainted with Mohl's 

 observations. That Link*, in the year 1841, should speak of antheridia 

 in a work where one might expect to find not only a complete use made 

 of the materials at the author's command, but likewise a thorough inves- 

 tigation of the subject treated of, makes one almost envy the man who 

 knows how to make work a matter of so little moment. Meyen says 

 nothing of this subject, the Lycopodiacece and Equisetacece not being 

 treated of in his system of Physiology. 



112. The stem of the Equiseta consists of a somewhat lax par- 

 enchyma, separated by a circle of from six to ten successive closed (?) 

 vascular bundles ( 26.) into medulla and cortex. In the under- 

 ground stem the external cortical cells become by degrees more 

 tough in the walls, and porous. Air-cavities occur alternately with 

 every two vascular bundles, formed in the cortex by tbe laceration 

 and resorption of the cellular tissue. A similar opening occurs in 

 the axis of the medulla. The vascular bundles are developed from 

 within outward, contain, most internally annular vessels, then spiral 

 vessels, and finally porous vessels. The first portion formed soon 

 dies off, the cells tear, and thus an air-hole is formed in the vascular 

 bundle itself; and we often find the annular or spiral vessels pro- 

 jecting into this aperture, or their remains fallen into it. In the 

 furrowed stems there lie upon the projecting ridges bundles of thick- 

 walled, elongated (liber) cells ; such a layer often appearing under the 

 whole epidermis of the stem, as, for instance, in Equisetum fluviatile. 

 The vascular bundles at the nodes range themselves closely into 

 a circle, and give off from here twigs, which pass into the leaves 

 and lateral branches. The parenchyma at the nodes has also 

 smaller and closer cells. The leaves have one vascular bundle, 

 and on their outer surface one bundle of liber ; and between the 

 two w T e find an air-passage. Their free unjoined extremities 

 are mostly, with the exception of the middle part, composed 

 of two thin cellular layers, dry and membranous. They are 

 furnished in the middle, like the stem itself, with an exceedingly 

 firm epidermis, which distinctly exhibits stomata, arranged mostly 

 in rows, and whose cells are for the most part thickened towards 

 the exterior in a wart -like manner. In the cellular walls, especially 

 in these wart-like projections, we find deposited a large quantity 

 of silica, in the form of small lamellae, which may be isolated by 

 means of concentrated sulphuric acid, which only destroys the vege- 

 table substance ; they unite, however, on being heated from the 

 action of the potash salts present, and then retain in the ashes the 

 perfect forms of the living plants.f The inner layer of the wall 

 of the sporocarp is formed of the most beautiful spiral fibrous cells. 

 The spherically enlarged stems below the surface contain, in a close 

 cellular tissue, starch (?) and oil, and have only very small, imper- 

 fectly developed vascular bundles. 



* Link, Filicuni Species, &c., p. 9. 



f Struve, De Silicia in Plantis nonnulla. Berlin, 1835. 



