The structure & development of the mosses and ferns (Archegoniatae) . rginianuvi than in OpJiio-glossum, and can be more easily followed, although here, too,as the division evidently proceeds very slowly, it is difficult totrace the limits of the segments beyond the first complete set,which in transverse section are sufficiently clear. The firstdivision divides the segment into an inner and an outer cell, 1 nolle (I), PL IV. Fig. 32. 244 MOSSES AND FERNS CHAP. the former probably being directly the initial fof the pleromecylinder. The outer cell by later divisions forms the cortex,and the epid
The structure & development of the mosses and ferns (Archegoniatae) . rginianuvi than in OpJiio-glossum, and can be more easily followed, although here, too,as the division evidently proceeds very slowly, it is difficult totrace the limits of the segments beyond the first complete set,which in transverse section are sufficiently clear. The firstdivision divides the segment into an inner and an outer cell, 1 nolle (I), PL IV. Fig. 32. 244 MOSSES AND FERNS CHAP. the former probably being directly the initial fof the pleromecylinder. The outer cell by later divisions forms the cortex,and the epidermis which covers the very small exposed surfaceof the stem apex. Here, as in Ophioglossum, it is impossibleto determine exactly the method of origin of the young leaves,one of which probably corresponds to each segment of theapical cell, but as soon as the leaf can be recognised as suchit is already a multicellular organ. It grows at first by anapical cell which seems to correspond closely in its growthwith that of the stem. From almost the very first (Fig. i 24). Fig. TZ^.—Boirychiuvi Virginianum (Sw.). A, Longitudinal section of the stem apex of a youngplant, X 260 ; B, cross-section of a similar specimen ; L, the youngest leaf. the growth of the leaf is stronger on the outer side, and inconsequence it bends inward over the stem apex. The arrangement of the tissues of the fully-developedstem shows, as we have seen, a striking similarity to thosein the stems of many Spermaphytes. The xylem of thestrictly collateral bundle is made up principally of largeprismatic tracheids (Fig. 125), whose walls are marked withbordered pits not unlike those so characteristic of the Coni-ferae, but somewhat intermediate between these and theelongated ones found in most Ferns. The walls betweenthe pits are very much thickened, and the bottoms of VIII THE PTERIDOPHYTA—OPHIOGLOSSACEJZ 245 corresponding pits in the walls of adjacent trachcids areseparated by a very delicate membrane. At inter
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Keywords: ., bookcentury1800, bookdecade1890, bookidstructuredev, bookyear1895
