^74 



MOSSES AND FERNS 



CHAP. 



the central ones. Numerous rhizoids of a peculiar structure 

 grow from the basal part of the stem, and from these, new 

 branches arise which replace the older ones as they die away. 

 These rhizoids are not simple rows of cells as in the Bryinese, 

 but are either cylindrical masses of cells or flattened plates. 

 These penetrate into the crevices of the rocks, or apply them- 

 selves very closely to the surface, so that the plants adhere 

 tenaciously to the substratum. 



Spores and Protonema 



The germination of the spores and the development of 

 the protonema show numerous peculiarities. The spores may 



B 



Fig. 83. — A, B, Germinating spores oi A. ^eirojihila, X 200 ; C, protonema with bud {k) ; D. young 

 archegonium in optical section ; E, i, 2, two views of a very young embryo of A. crassmerva, 

 X 266 ; F, somewhat older embryo of ^. petrophila ; G, older embryo showing the first archesporial 

 cells; H, I, cross-sections of young embryos, X 200. A-D, after Kiihn ; E-I, after Waldner. 



germinate within a week, or sometimes remain unchanged for 

 months. They have a thick dark-brown exospore and contain 

 chlorophyll and oil. The first divisions take place before the 

 exospore is ruptured, and may be in three planes, so that the 

 young protonema then has the form of a globular cell mass 

 (Fig. 83, A). This stage recalls the corresponding one in 

 many of the thallose Hepaticae, e.g. Peliia, Radtda, and is 

 entirely different from the direct formation of the filamentous 

 protonema of most Mosses. Some of the superficial cells of 

 this primary tubercle grow out into slender filaments, either 

 with straight or oblique septa, and these later ramify exten- 



