. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 48 MOSSES AND FERNS carpus, the original air-chambers become divided by the devel- opment of partial diaphragms into secondary chambers, which are not, hovirever, arranged in any regular order, .and communi- cate more or less with one another. In Targionia (Figs. i8, 19), where the archegonia are borne upon the ordinary shoots, the growth of the dorsal seg- ments is so much greater than that of the ventral ones that the upper part of the thallus projects far beyond the growing point, j^ which
. The structure and development of mosses and ferns (Archegoniatae). Plant morphology; Mosses; Ferns. 48 MOSSES AND FERNS carpus, the original air-chambers become divided by the devel- opment of partial diaphragms into secondary chambers, which are not, hovirever, arranged in any regular order, .and communi- cate more or less with one another. In Targionia (Figs. i8, 19), where the archegonia are borne upon the ordinary shoots, the growth of the dorsal seg- ments is so much greater than that of the ventral ones that the upper part of the thallus projects far beyond the growing point, j^ which is pushed under toward the ventral side. A similar condition is found in the archegonial receptacles of other forms, where this in- cludes the growirig point of the shoot (Fig. 21). In Targionia the lacunae are formed much as in Fimbriaria, but they are shallower and much wid- er, and the pores corre- spondingly few. The as- similative tissue here re- sembles that of Mar- thantia and others of the higher forms. It is sharply separated from the compact colourless tissue lying below it, and the cells form short con- fervoid filaments more or less branched and an- astomosing, and except in the central part of the chamber united with the epidermal cells. Under the pore, however, the ends are free and enlarged with less chlorophyll than is found in other cells. All of the Marchantiese except the aberrant genera Dumor- tiera and Monoclea correspond closely to one or the other of the above types in the structure of the thallus, but in the latter the air-chambers are either rudimentary or completely absent, and the ventral scales are also wanting. Leitgeb ( (7), vi., p. 124). Fig. j^.—Fimbriaria Californica. A, Vertical sec- tion throueh the apex of a sterile shoot, show- ing the formation of the air-chambers ; x, the apical cell, X300; B, similar section through an older part of the thallus, cutting through a pore. X100,. Please note that these images are extracted from scanned page
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