. The structure and development of mosses and ferns (Archegoniatae). them develops into the pro-thallium, the others dividing only once or twice, and formingshort brown rhizoids. In some species of Trichomanes^ e. g. *The number of species known now considerably exceeds this. 374 MOSSES AND FERNS CHAP. T. pyxidiferum (Bower (8)), the prothallium remains fila-mentous, and forms a densely branching structure very muchlike the protonema of some Mosses, but coarser in species, however, e. g., T. alatum, produced flattenedthalloid prothallia from branches of the filamentous forms, and
. The structure and development of mosses and ferns (Archegoniatae). them develops into the pro-thallium, the others dividing only once or twice, and formingshort brown rhizoids. In some species of Trichomanes^ e. g. *The number of species known now considerably exceeds this. 374 MOSSES AND FERNS CHAP. T. pyxidiferum (Bower (8)), the prothallium remains fila-mentous, and forms a densely branching structure very muchlike the protonema of some Mosses, but coarser in species, however, e. g., T. alatum, produced flattenedthalloid prothallia from branches of the filamentous forms, andHymenophyllum always has a flat hepatic-like prothallium,which in its earHer stages, according to Sadebeck ((6), ), always develops a two-sided apical cell, and differs in nowise from that of other Ferns. These prothallia, however,remain single-layered throughout, although they reach an ex-traordinarily large size, and branch much more freely thanthose of most other Ferns (Fig. 215). The rhizoids arealways very short and dark-coloured, and generally occur in. s Fig. 2IS-—Hymenophyllum (sp). A, Large prothallium of the natural size; B, part ofthe margin of one of the growing branches, showing two similar initial cells, Xi8o;C, a filamentous male prothallium derived from a bud, X6o. groups upon the margin only. The branching of the prothalliais either monopodial or dichotomous, and the latter methodmay be repeated a number of times. They may live for an in-definite time apparently. The writer has kept prothallia ofboth Trichomanes and Hymenophyllum for nearly two years,at the end of which time they showed no diminution of form ordinary adventitious shoots, but there are alsospecial gemmae developed in many of them, often in great num-bers. In an undetermined species of Hymenophyllum col-lected In the Hawaiian Islands (Fig. 216) these gemmae oc-curred very abundantly upon prothallia that had ceased to formsexual organs. A marginal cell grows out and curves upwar
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