The structure & development of the mosses and ferns (Archegoniatae) . ^ Lachmann (7), p. 118. 2 Bovver (11), p. 362 ; Goebel (17), p. 387. XI THE HOMOSPOROUS LEPTOSPORANGIAT^ 357 the tetrahedral form of the true Leptosporangiatcs, but shows agood deal of variation. As in these the wall of the sporangiumis only one-layered, and the tapetum ordinarily two, butoccasionally three-layered. The fully-developed sporangium isin shape much like that of BotrycJiium Virginianum, and hasa very short massive stalk. Like HehnintJiostacJiys andAngiopteris, it opens by a vertical cleft, and like the latterthe
The structure & development of the mosses and ferns (Archegoniatae) . ^ Lachmann (7), p. 118. 2 Bovver (11), p. 362 ; Goebel (17), p. 387. XI THE HOMOSPOROUS LEPTOSPORANGIAT^ 357 the tetrahedral form of the true Leptosporangiatcs, but shows agood deal of variation. As in these the wall of the sporangiumis only one-layered, and the tapetum ordinarily two, butoccasionally three-layered. The fully-developed sporangium isin shape much like that of BotrycJiium Virginianum, and hasa very short massive stalk. Like HehnintJiostacJiys andAngiopteris, it opens by a vertical cleft, and like the latterthere is a rudimentary annulus consisting of a group of thick-walled cells (Fig. 184, r). The GleidieniacecE These comprise about twenty-five species of tropical andsub-tropical Ferns, which may be all placed in two genera ^—. Fig. 185.—A, Pinnule of Glcichenia dichotoma (Willd.), showing the position of the sori (s), X4 ; B,ventral ; C, dorsal view of the ripe sporangium, X 85 ; D, vascular bundles of the petiole andstem of Gleichenia (sp.) (after Poirault). The dark masses represent the xylem masses; ph,phloem ; en, endodermis. Platyzoma, with a single species P. luicrophyllum, and best known is G. dicJwtoma, an extremely common Fern of ^ Hooker and Baker (1) 358 MOSSES AND FERNS chap. the tropics of the whole world. It has very long leaves, whichfork repeatedly, and may be proliferous from the growth of budsdeveloped in the axils of the forked pinnae. The development of the prothallium has been studied byRauwenhoff,^ and shows some interesting points in which it isintermediate between the Osmundaceae and the other Leptospor-angiatae. The spores of Gleichenia are usually tetrahedral, andcontain no chlorophyll. When the ripe spores are sown, after afew days the oil-drops become much small
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