. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 330 MOSSES AND FERNS chap. In Onoclea struthiopteris, as in most leptosporangiate Ferns, the outer cortical cells become changed into sclerenchyma. The sclerenchyma forms several hypodermal layers, distinctly separated from the inner cortical parenchyma. These scler- enchyma cells are much elongated; their lateral walls are some- what uneven, and in their younger stages swell up more strongly under the action of potassic hydrate than do the cortical cells. Their walls become thick, are first p
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 330 MOSSES AND FERNS chap. In Onoclea struthiopteris, as in most leptosporangiate Ferns, the outer cortical cells become changed into sclerenchyma. The sclerenchyma forms several hypodermal layers, distinctly separated from the inner cortical parenchyma. These scler- enchyma cells are much elongated; their lateral walls are some- what uneven, and in their younger stages swell up more strongly under the action of potassic hydrate than do the cortical cells. Their walls become thick, are first pale yellow, and later a dark reddish brown. The walls are very markedly striate, and the central lamella distinct. Deep pits extend down to the latter. The bundles in the stems of the Polypodiacese are very uniform in structure. They are usually elliptical in section, and the first tracheary tissue formed is a strand of small spiral, or reticulate tracheids at the foci of the bundle. From there the formation of the very large scalariform ones, so character- istic of the leptosporangiate Ferns, proceeds towards the centre of the bundle, where the last-formed ones are situated. The young tracheids have thin walls and abundant protoplasm, but as the wall thickens, the contents gradually disappear, and. Fig. 182.—Polypodium falcatum; A, Transverse section of the rhizome, X6; B, d sin- gle vascular bundle, Xi7S; en, endodermis. finally no living protoplasm remains in them. Faint elongated transverse pits become evident, and the spaces between these rapidly thicken at the expense of the cell contents until all the protoplasm is used up. The thickened bars between the pits give the characteristic ladder-like appearance to the older. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Campbell, Douglas Houghton, 1859-
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