File:The structure and development of mosses and ferns (Archegoniatae) (1918) (14598275529).jpg

Identifier: structuredevelop00camp3 (find matches)
Title: The structure and development of mosses and ferns (Archegoniatae)
Year: 1918 (1910s)
Authors: Campbell, Douglas Houghton, 1859-1953
Subjects:
Publisher: New York, Macmillan
Contributing Library: The LuEsther T Mertz Library, the New York Botanical Garden
Digitizing Sponsor: The LuEsther T Mertz Library, the New York Botanical Garden

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cell. From the outer cellsof the dorsal segments the sexual organs arise, and from thoseof the ventral segments the overlapping lamellae upon the lowersurface of the thallus, and also the rhizoids. The rapiddivision of the inner cells of the segments, especially those ofthe dorsal ones, causes the thallus to become rapidly thickerback of the apex. Sections made parallel to the surface of thethallus, and passing through the growing point (Fig. 3), show II MUSCINEAL—HEPATIC^—MARCH ANTI ALES 25 that the margin is occupied by a group of cells that look verymuch alike. Sometimes one of these cells is somewhat largerthan the others, but more commonly it is impossible to decidewith certainty that a single initial is present. From a com-parison of the two sections it is at once evident that the initialcells have nearly the form of the segment of a disc, and that inaddition to the dorsal and ventral segments lateral ones are cutoff as well. In the region just back of the apex the tissue of
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Fig. 2.—Riccia glauca. Development of the archegonium, XS^S- A, Vertical sectionthrough the growing point; x, apical cell; ar, young archegonium; //, ventrallamellae; B-F, successive stages in the development of the archegonium, seen inlongitudinal section; G, cross-section of young archegonium (diagrammatic). the thallus is compact, but in the older parts a modification isobservable both on the dorsal and ventral surfaces. In theformer, a short distance from the growling point, the superficialcells project in a papillate manner above the surface. Thiscauses little depressions or pits to be formed between the adja-cent cells (Fig. 3, C). The subsequent divisions in the papillaeare all transverse, and this transforms each papillate surface cellinto a row of cells which, as it elongates, causes the pitsbetween it and the adjacent ones to become deep but narrowair-channels, so that in the older parts of the thallus the upperportion is composed of closely-set vertical rows of chlorophyl

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