164 



SECOND GROUP. MUSCINEAE. 



protonema and in the structure of the sporogonium. The spores of Sphagnum, at 

 least when they germinate on a firm substratum, produce a flatly expanded tissue, 

 which branches to form a crisped margin and gives rise to leafy stems. In Andreaea 

 the contents of the spore divide, according to Kiihn's observations, while still 

 within the closed exosporium into four or more cells, thus forming a tissue such as 

 is found in the spores of many Hepaticae, as Radula and Frullanid*- \ ultimately 

 one to three peripheral cells develope into filaments which spread out on the stony 

 substratum. The branches of the protonema may then develope further in three 

 ways ; they either undergo longitudinal division in addition to the cross-divisions and 

 so form ribbon-like irregularly branching cell-surfaces, or divisions parallel to the 

 surface also make their appearance and the protonema comes to be of more than one 

 layer of cells, and having thus become a body of cellular tissue grows erect and 

 branches like a tree or shrub ; a third form is where the branches of the protonema 



FIG. 116. Funaria hygrometrica. A germinating spore; v vacuole, w rhizoid, s exosporium. B portion of a de- 

 veloped protonema, about three weeks after germination ; h a prostrate primary shoot with brown wall and obliquely 

 transverse septa, from which proceed the ascending branches with limited growth ; at /f the rudiment of a leafy axis with 

 rhizoid w. A magn. 350 times, B about 90 times. 



are leaf-like flat bodies of tissue with simple definite outline. There is -some 

 resemblance between these expanded protonemata and the cell-surfaces which form 

 assimilating organs of the protonemata of Tetraphis and Tetradontium, and which, as 

 is shown in a figure further on, are formed at the end of long slender protonema- 

 filaments. Oedopodium too and Diphyscium have similar protonemata 2 . Peculiar 

 formations are found also on the felted rhizoids of tufts of Diphyscium foliosum, 

 where branches arise on the protonema formed from the rhizoids, which either 

 develope into a cell-surface, or more frequently bear a cell-surface on a stalk which in 

 cross section is seen to be formed of several cells ; their apex spreads out into a cell- 

 surface, which is sometimes at length concave above and is placed on a stalk of 



1 In true Mosses (Bartramia, Leucobryum, Mnium, Hypnum), the first transverse wall of the 

 filament sometimes makes its appearance inside the spore (Kiihn). 



2 Bot. Jahresber. 1874, p. 312. 



