FILICINEAE. HOMOSPOROUS F1LICINEAE. 



201 



only imperfectly known. The prothallium of Hymenophylhtm tunbridgense, according 

 to Janczewski and Rostafinski, differs from the forms described above chiefly in being 

 composed of one layer of cells, and in having therefore no cushion on the under side. 

 The cell-walls are thick and pitted ; the rhizoids are all marginal. The antheridia 

 are placed on the under side of the prothallium. The archegonia are in groups on 

 the margin of the prothallium, and their longitudinal axis is at right angles to the 

 surface of the prothallium ; some archegonia in a group are directed upwards, some 

 downwards. The embryo forms a root, but the older plant has none. The variations 

 in this case concern chiefly the position of the archegonia. The first stages of 

 germination may be seen in the spores while they are still in the sporangium, or in 

 the cup-shaped indusium. The spore in Hymenophyllum divides before the rupture 

 of the exosporium into three cells, one of which developes into the filamentous 

 prothallium, the others into hair-like forms and soon cease to grow. Many of the 

 Hymenophyllaceae form at first a much branched confervoid protonema, on which 

 flat prothallia of from four to six lines in length and from one half to one and a half 

 lines in breadth are produced as lateral shoots. Each cell of the filament can give 

 rise to a branch, which appears behind the anterior transverse wall and is at once cut 

 off by a septum. Some of these branches, like 

 the mother-shoot, have unlimited growth, others 

 end in hair-like processes, a larger number still 

 develope into the flat prothallia just mentioned, 

 but most of them become rhizoids ; occasionally 

 the rudiment of a branch may develope into an 

 antheridium or even an archegonium. Round 

 cells, which are probably organs of propagation, 

 appear in Trichomanes insitnm on flattened mar- 

 ginal cells at the apex of the flat prothallia. Only 

 the marginal cells of these prothallia can develope 

 into rhizoids and new protonema-filaments, and 

 also into new flat shoots. The rhizoids are 

 generally short with brown walls, and form at 

 their extremity lobed disks of attachment or 

 tubular branches. 



In the Schizaeaceae 1 also the formation of 

 the prothallium agrees in the main points with 

 that of the Polypodiaceae. Aneimia Phyllitidis 



maybe taken as a suitable example. Fig. 149 shows that the growing point (sK) is 

 not at the apex but at the side of the prothallium ; and the prothallium is not 

 cordate, there is only one lobe forming the extremity of the prothallium, the other 

 being indicated only by a slight projection. The growing point of the prothallium 

 is sometimes lateral in the Polypodiaceae also. 



The anlheridia, like the rhizoids, are outgrowths of the marginal or of the surface 



FIG. 149. Aneiitiici Phyltitidis, Prothallium 

 seen from below ; s apex of the cushion of tissue on 

 which a few archegonia may be seen, a antheridia 

 with rhizoids on the margin and surface of the lower 

 part of the prothallium. After Bauke, magn. 25 

 times. 



u. Rostafinski, Note sur le prothalle de I' Hymcnophylhim tunbridgense (Mem. de la Soc. nat. de 

 Cherbourg, 1875). Prantl, Unters. ii. d. Gefasskryptogamen, Heft I. 



1 Bauke, Beitr. z. Keimungsgesch. d. Schizaeaceen in Prings-heim's Jahrb. Bd. XI, where other 

 works are cited. Prantl, in Flora, 1878, p.. 12 of the reprint. 



