i68 



MOSSES AND FERNS 



CHAP. 



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 very 

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

 substratum, forms a flat thallus, which at first sometimes grows 



by a definite apical cell (C. 

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

 late shape (Fig. 87, A, B), which 

 later becomes broadly heart-shaped, 

 and closely resembles in this condi- 

 tion a young Fern prothallium, for 

 which it is readily mistaken. The 

 older ones become more irregular 

 and may attain a diameter of sev- 

 eral millimetres. The thallus is 

 but one cell thick throughout its 

 whole extent, and is fastened to the 

 earth by colourless rhizoids. Later 

 similar filaments grow out from the 

 marginal 1 cells of the thallus, and a 

 careful examination shows that 

 they are septate, and closely re- 

 semble the protonemal filaments of 

 other Mosses. Like those, the 

 septa, especially in the colourless 

 ones, are strongly oblique. These 

 marginal protonemal threads may, 

 according to Hofmeister (i) and 

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

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

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

 tion of a flat thallus is suppressed and the protonema remains 

 filamentous, but Goebel disputes this. 



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

 from each thalloid protonema, and although this is not expressly 

 stated by Hofmeister and Schimper, their figures would indi- 

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



Fig. 88. — Sphagnum squarrosum. 

 Leafy shoot with sporophytes 

 (sp), borne at the end of leaf- 

 less branches, or "pseudopodia," 



X2. 



