. The structure and development of mosses and ferns (Archegoniatae). hich ap-proaches more or less the tetrahedral form of the true Lepto-sporangiates, but shows a good deal of variation. As in thesethe wall of the sporangium is only one-layered, and the tapetumordinarily two, but occasionally three-layered. The fully-de-veloped sporangium is in shape much like that of BotrychiumVirginianum, and has a very short massive stalk. Like Hel-minthostachys and Angiopteris, it opens by a vertical cleft, andlike the latter there is a rudimentary annulus consisting of agroup of thick-walled cells (Fig.
. The structure and development of mosses and ferns (Archegoniatae). hich ap-proaches more or less the tetrahedral form of the true Lepto-sporangiates, but shows a good deal of variation. As in thesethe wall of the sporangium is only one-layered, and the tapetumordinarily two, but occasionally three-layered. The fully-de-veloped sporangium is in shape much like that of BotrychiumVirginianum, and has a very short massive stalk. Like Hel-minthostachys and Angiopteris, it opens by a vertical cleft, andlike the latter there is a rudimentary annulus consisting of agroup of thick-walled cells (Fig. 207, r). The GleicheniacetE These comprise about twenty-five species of tropical and sub - tropical Ferns,which may be all placedin two genera (Di^ls(I))— Stromatopteris,with a single species andGleichenia with about25 species. The bestknown is G. dichotoma,an extremely commonFern of the tropics ofthe whole world. It hasvery long leaves, whichfork repeatedly, andmay be proliferous fromthe growth of buds de-veloped in the axils ofthe forked X4; Fig. 208.—Gleichenia pectinata. Prothallia, B, a large prothallium seen from below, show-ing a dichotomy of the apex; C, the youngsporophyte attached to the prothallium. The Gametophyte The development of the prothallium has been studied byRauwenhoff ( i), and shows some interesting points in which itis intermediate between the Osmundacese and the other Lep-tosporangiatse. The spores of Gleichenia are usually tetra- THE HOMOSPOROUS LEPTOSPORANGIATJE 367 hedral, and contain no chlorophyll. When the ripe spores aresown, after a few days the oil-drops become much smaller butmore numerous, and the first chloroplasts become latter increase in number and size, and small starch grainsare developed. The exospore is ruptured in from two to threeweeks from the time the spore is sown, and the spore contentssurrounded by the intine project through the opening. Thefirst wall usually separates the first rhizoid,
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