EQUISETINEAE. 



259 



gives rise to the rudimentary stem with a three-sided pyramidal apical cell, two others 

 produce one cotyledon, and the fourth the second cotyledon ; these cotyledons, how- 

 ever, do not develope as separate leaves, for they unite as they grow at a very early 

 period with the first leaf which proceeds from the apex of the stem, to form an 

 annular wall. The root and the foot are formed from the hypobasal half of the 

 embryo, just as in the Filicineae. 



The first leafy shoot grows upwards and forms from ten to fifteen internodes 

 with foliar sheaths, each with three teeth ; it soon produces at its base a new and 

 stronger shoot having sheaths with four teeth (E. arvense, E. pratense, JE. variegatum, 

 Hofmeister), and this again gives rise to new generations of shoots constantly 

 developing -thicker stems and sheaths with more numerous teeth ; sometimes the 

 third or one of the succeeding_ shoots strikes downwards into the ground and forms 

 the first persistent rhizome, which then 

 produces fresh underground rhizomes and 

 ascending leafy shoots from year to year. 



To facilitate the understanding of the 

 growth of the stem and leaves, we must 

 first examine their structure in the fully 

 developed state. Every shoot consists of 

 a series of segments of the axis or inter- 

 nodes, which are usually hollow and closed 

 at their base by a thin transverse septum or 

 diaphragm ; each of these internodes passes 

 upwards into a foliar sheath which em- 

 braces the next internode, and the sheath 

 divides at its upper margin into three or 

 four or usually more teeth. A vascular 

 bundle runs downwards in a straight line 

 from each tooth into the internode as far as 

 the node at its base, and parallel with the 

 rest of the bundles of the internode ; at its 

 lower end each bundle splits into two 

 short diverging arms, by means of which it 



unites with the two adjacent bundles of the next internode below, where they descend 

 into it from their sheath-teeth ; in this way the stem-segments or internodes with their 

 foliar sheaths alternate, and as in every segment the arrangement of the bundles, 

 jbliar teeth, projecting longitudinal ridges and furrows, is repeated with exact regu- 

 larity in the transverse section, the formations in one segment always coincide with 

 the intervals between the homologous formations in the next* segment above and 

 below. If, for example, the internode shows a longitudinal ridge projecting on its 

 surface, a similar ridge runs down from the tip of each foliar tooth parallel with the 

 other as far as the base of the internode; between every two teeth begins a furrow or 

 channel, which also continues on to the base of the internode. The projecting ridges 

 are on the same radii as the vascular bundles, which contain each an air-space, the 

 carinal canal ; the depressions or furrows lie on the same radii as the lacunae of the 

 cortical tissue (vallecular canals), though these are sometimes wanting, and alternate 



S 2 



FIG. 212. Development of the embryo of Equisetum 

 arvense, according to Hofmeister. A archegonium cut through 

 vertically with the embryo, bolder embryo isolated ; b annular 

 leaf-cushion formed by union of the two cotyledons and the 

 first leaf of the steni, s apex of the first shoot. C vertical section 

 of a lobe of the prothallium // with a young plant ; w the 

 first root, b t b' the leaf-sheaths. A and B magn. 200, C 20 

 times. 



