i68 



MOSSES AND FERNS 



CHAP. 



sp 



show no trace of a midrib. As the axis elongates the leaves 

 become separated, as well as the lower branches, but upon the 

 smaller branches they remain closely imbricated. Rhizoids 

 are present only in the earlier stages of the plant's growth, and 

 are only occasionally found in a very rudimentary condition in 

 the older ones. 



The spores of Sphagnum on germination form first a ver^ 

 short filament, which soon, at least when grown upon a solid 

 substratum, forms a flat thallus, which at first sometimes gro^^s 



by a definite apical cell (C. 

 Muller (3)). It first has a spati- 

 late shape (Fig. 87, A, B), whi::h 

 later becomes broadly heart-shapec, 

 and closely resembles in this cond- 

 tion a young Fern prothallium, for 

 which it is readily mistaken. Tie 

 older ones become more irregular 

 and may attain a diameter of se]- 

 eral millimetres. The thallus s 

 but one cell thick throughout i's 

 whole extent, and is fastened to tte 

 earth by colourless rhizoids. Lat(r 

 similar filaments grow out from tie 

 marginal cells of the thallus, and a 

 careful examination shows th;t 

 they are septate, and closely n- 

 semble the protonemal filaments tf 

 other Mosses. Like those, tie 



Fig. 8S. — Sphagnum squarrosum. ggp^^ especially lU the COloUrlciS 

 Leafy shoot with sporophytes ^ ^ -^ 



{sp), borne at the end of leaf- oucs, are strongly obliquc. 1 hce 

 less branches, or "pseudopodia," marginal protoucmal threads mat, 



according to Hofmeister ( i ) anl 

 Schimper (i), produce a flattened thallus at their extremitj, 

 and thus the number of flat thalli may be increased. Schimpir 

 states that if the germination takes place in water, the formj- 

 tion of a flat thallus is suppressed and the protonema remaiis 

 filamentous, but Goebel disputes this. | 



In the few cases observed by me, only one leafy axis aros 

 from each tlialloid protonema, and although this is not express^ 

 stated by Hofmeister and Schimper, their figures would ind- 

 cate it. At a point, usually near the base, a protuberance $ ^ 



