The structure & development of the mosses and ferns (Archegoniatae) . originates upon the uppersurface of the sporophyll close to its base, and in radial sectionthe young sporangium appears to originate from a single cell;but this is really only one of a transverse row of cells, all ofwhich participate in its formation. Each cell of this primaryrow divides first into a large central cell (Fig. 249, C, x) and(in radial section) two peripheral ones. The central cell nextby successive periclinals forms a row of three cells, of which themiddle one is the archesporium, which, judging only from radi


The structure & development of the mosses and ferns (Archegoniatae) . originates upon the uppersurface of the sporophyll close to its base, and in radial sectionthe young sporangium appears to originate from a single cell;but this is really only one of a transverse row of cells, all ofwhich participate in its formation. Each cell of this primaryrow divides first into a large central cell (Fig. 249, C, x) and(in radial section) two peripheral ones. The central cell nextby successive periclinals forms a row of three cells, of which themiddle one is the archesporium, which, judging only from radialsections, seems to consist only of a single cell ; but comparingwith the radial section a tangential one, it is seen that thearchesporium really consists of a row of similar cells (Fig. 249,F). The growth in the upper part of the sporangium isstronger than below, so that a distinct, although short stalk isformed. The archesporial cells rapidly divide, but show little ^ Plegelmaier (i).- Bower (15) ; also Goebel (3), Bot. Zeit. 18S0, p. 561 ; Sadebeck (6), p. Fig. 249.—A, Plant oi Pliylloglossiiin Drttimnondii (V,.\ix\zft), X about 3 (after Bertrand). sp. Spor-angia ; R, roots ; Tl, protocorm ; T^, secondary protocorm ; B, longitudinal section of the youngstrobilus of the same, showing the initial cell (/), young leaves (/, /), antl young sporangium (jr/),X240; C-E, young sporangia of Aj/co/t^i/^KW .ff/rt^o, radial sections, X225; F, tangential sectionof the same ; G, radial section of young sporangium of L. clavatum (Figs. B-G after Bower). 478 MOSSES AND FERNS chap. regularity in the divisions. All of the resulting cells separateand produce four spores in the usual manner. The wall of themature sporangium consists regularly of three layers of cells, ofwhich the innermost is the tapetum. The tapetum boundingthe lower part of the archesporium is derived from the cushion-like group of cells below it, to which Bower gives the name sub-archesporial pad. The tapetum does n


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Keywords: ., bookcentury1800, bookdecade1890, bookidstructuredev, bookyear1895