362 



MUSCINEM. 



Mosses both in the structure of the sporogonia, and in the mode of formation of 

 the protonema. The spores of the Sphagnaceae produce, at least when they grow 

 upon a firm substratum, a, flatly expanded plate of tissue, which branches at the 

 margin, and produces from its surface the leafy stems. In AndrccEa, according 

 to the investigations of Kiihn, the contents of the spore divide, while still within 

 the closed exospore, into four or more cells, and a tissue is thus formed similar to 

 that produced in the spores of some Hepaticae (as Radula and FruUanid) ^ : finally, 

 from one to three peripheral cells grow into filaments which extend over the 

 hard stony substratum. The branches of the protonema may now develope further 

 in three different ways; longitudinal as well as transverse divisions arise, and 

 irregularly branched cellular ribbons are formed; or, divisions also taking place 

 in addition parallel to the surface of these ribbons so that they come to be several 

 layers thick, the protonema developed in this manner as a mass of tissue becomes 



Fig. 247. — h'unaria hygrotnetrica ; A germinating spores; v vacuole; iv root-hair; J exospore; B part of a developed 

 protonema, about three weeks after germination ; h a procumbent primary shoot with brown wall and oblique septa, out 

 of which arise the ascending branches with limited growth ; K rudiment of a leaf-bearing axis with root-hair w (^ x 550 ; 

 B about 90). 



erect and branches in an arborescent manner ; finally, in the third form, the leaf-like 

 branches of the protonema are plates of tissue of simple definite outline. Closely 

 allied to this last form is the flat protonema of Tetraphis and Tetradontium, which, 

 as will be further shown in a following illustration, arises at the end of longer and 

 slenderer filaments'^. 



The buds which develope into the Moss-stems apparently never arise at the 

 end of one of the principal protonemal filaments, but as lateral branches upon 

 them. The idea suggested by me that the protonema, as also the equivalent 

 rhizoids of the Bryineae, represent a very rudimentary much elongated Moss-stem, 

 just as the branches with naked base of Chara are merely simple forms of its 

 stem, has been proved correct by the observations of Schuch (i 870-1871) made 



* In true Mosses also (as Bartramia, Leucohryum, Mnium, and Hypmtm) the first septum of the 

 protonema is formed, according to Kiihn, even within the spore. 

 ^ Compare Berggren, Bot. Zeitg. 1871. 



