. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. FILICINE^ LEPTOSPORANGIAT^ 337 en. first-formed cap cell (or "epidermal segment," to use his termin- ology), there is, in the central part, always a doubling of the cells by periclinal walls, so that each layer of the older root-cap is normally double, except sometimes at the extreme edge. There is very little displacement of the cells for a long time, and cross-sections of the root, made some distance below the summit, still show the Hmits of the original sextant walls, which form s
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. FILICINE^ LEPTOSPORANGIAT^ 337 en. first-formed cap cell (or "epidermal segment," to use his termin- ology), there is, in the central part, always a doubling of the cells by periclinal walls, so that each layer of the older root-cap is normally double, except sometimes at the extreme edge. There is very little displacement of the cells for a long time, and cross-sections of the root, made some distance below the summit, still show the Hmits of the original sextant walls, which form six radiating lines with periclinal walls arranged with great regularity. In the centre the divisions proceed with great rapidity, and the plerome soon shows the elongated narrow pro- cambium cells. In the centre are four much larger cells, which develop later into tracheids, and three of these can be traced back to the central cells of the three larger sex- tants (Fig. i88, D) ; the fourth arises from the in- ner cell of one of the smal- ler ones. This central group of cells marks the position of the plate of tracheary tissue, found later in the root. By this time the parts of the com- plete root are all indicated. The bundle is bounded externally by the endo- dermis, whose cells are much elongated trans- versely, and clearly dis- tinguishable from the peri- cambium (pericycle), which consists of one or two rows of cells. Inside this is the mass of procambium cells, the large tracheids of the central part of the xylem being very evident (Fig. 188, E). The masses of procambial cells on either side of this central line of cells constitute the young phloem. The primary tracheids (protoxylem) arise simultaneously at the foci of the section, and consist of a single line of narrow pointed tracheids, with fine spiral markings, very closely set at first, but later pulled apart somewhat with the increase in length of the root. These are formed a long time before any other permanent tiss
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Keywords: ., bookauthorcampbelldouglashought, bookcentury1900, bookdecade1910
