313 



MUSCINEM. 



short term of life, as in the Phascaceae, Pottia, Physcomitrium, &c., the protonema 

 still remains vigorous after it has produced the leafy plants, and when the sporo- 

 gonium has already been developed upon them. In such cases all three stages of 

 the cycle of development are present simultaneously in genetic connexion. The 

 Sphagnaceae, Andreseaceae, and Tetraphidei differ from the typical Mosses both in 

 the structure of the sporogonia, and in the mode of formation of the pro-embryo. 

 The spores of the Sphagnaceae produce, at least when they grow upon a firm sub- 

 stratum, a flatly expanded plate of tissue, which branches in a crinkled manner at 

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

 to the most recent 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 from the spores of some Hepaticae (as Radula and Frul- 

 lania)'. Finally from one to three peripheral cells grow into filaments which 



Fig. izd.—Fujiaria hy^yotnetrica; A germinating spores ; v vacuole ; w root-hair ; s 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; A" rudiment of a leaf-bearing axis with loot-hair?^ (A XS50; 

 B about 90). 



expand over the hard stony substratum. The branches of this protonema may 

 now develope further in three different ways; longitudinal as well as transverse 

 divisions arise, and irregularly branched cellular ribbons are formed; or, divi- 

 sions also taking place in addition parallel to the surface of these ribbons, the 

 pro-embryos developed in this manner as masses of tissue become erect and 

 branch in an arborescent manner; finally, in a third form the leaf-like branches 

 of the pro-embryo are plates of tissue of simple definite outline. Closely allied 

 to this last form are the flat pro-embryos of Tetraphis and Tetradontium, which, 

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

 slenderer filaments of a protonema I 



^ In true Mosses also (as Bartramia, Leucobryum, Mnium, and Hypnum), the first septum of 

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

 2 Compare Berggren, Bot. Zeitg. 1872, nos. 23, 24. 



