THIRD GROUP. VASCULAR CRYPTOGAMS. 



with the vascular bundles. The branches and roots spring exclusively from inside the 

 base of the leaf-sheath, and as this is a whorl, the branches and roots are therefore 

 also arranged in whorls. The branches have the appearance as if of endogenous origin, 

 beino- formed on the inside of the basal tissue of the leaf-sheath on a radius of the stem 

 which falls between the vascular bundles, and therefore also between the teeth of the 

 sheath ; a root may be formed between each branch, and they both break through 



the base of the leaf-sheath. All the segments of the 

 stem agree in these points, whether they are developed 

 as underground rhizomes, as tubers, as ascending 

 stems, as leafy branches, or as sporangiferous shoots. 

 The end of the stem enclosed in a number of 

 young foliar sheaths culminates in a large apical cell, 

 the upper wall of which is strongly convex, while its 

 inferior and lateral bounding lines are almost plane ; 

 consequently the apical cell has the form of a three- 

 sided pyramid, the upturned base of which is an 

 almost equilateral spherical triangle. The segments 

 are cut off by walls which are parallel with the 

 oblique sides of the apical cell, that is, with the 

 youngest primary walls of the segments ; the seg- 

 ments, which are arranged with a spiral divergence 

 of one-third, lie in three straight rows. Each segment 

 is in form a three-sided tabular cell with an upper 

 and under triangular primary wall, a right and a left 

 quadrangular lateral wall, and a curved quadrangular 

 outer wall. Each segment divides first by an an- 

 ticlinal wall parallel with the primary walls into two 

 equal tabular cells lying on one another and half 

 the height of the original segment ; then usually each 

 half-segment is again halved by a nearly radial ver- 

 tical wall, the sextant wall. The segment now con- 

 sists of four cells, two of which lie one above the 

 other and extend to the centre, but the two others do 

 not, because the vertical wall (sextant wall) is not 



FIG. 213. Equisetidn Tfhnatfja. A piece 

 of an erect stem ; ;', ?' internodes, h its central 

 cavity, / lacunae of the cortex, 5 leaf-sheath, 

 z its apex, a, a' t a" the lower internodes of 

 slender leaf-shoots. B longitudinal section of a 

 rhizome ; k transverse diaphragm between the exactly 1'adial, but joillS Oil at itS inner did tO O116 



cavities h h, ^vascular bundle, / cortical la 

 cunae, 5 leaf-sheath. C transverse section of 

 a rhizome ; g and / as above. D union of vas- 

 cular bundles of an upper and a lower internode 

 i, i 1 ; A'the node. A natural size, B and C about 

 twice the nat. size. 



of the lateral walls of the segment (the anodal wall) 

 (Fig. 214 -E). Then follow divisions, but not in fixed 

 order, in the four cells of each segment parallel 

 with the primary and lateral walls, and soon after periclinal divisions appear by which 

 the segment is divided into inner and outer cells, and these are then subjected to further 

 divisions ; the inner cells form the pith, which is soon destroyed by the elongation of 

 the stem as far as the diaphragm at the base of each internode ; the outer cells 

 produce the leaves and the whole of the tissue of the hollow internodes. It has been 

 already stated that the segments as first formed are disposed in a spiral line with a 

 divergence of one-third, and since each segment without exception produces, as in the 

 Mosses, a leaf or a portion of a leaf-sheath, the leaves of the Equisetaceae must also 



