V. 



MOSSES (MUSCI): SPHAGNALES—ANDRE^ALES 183 



young protonema then has the form of a globular cell mass 

 (Fig. 95, A). This stage recalls the corresponding one in 

 many of the thallose Hepaticae, e. g., Pellia, Rachila, 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- 

 sively. Where there are crevices in the rock, some of these 

 branches grow into them as colourless rhizoids. but, as in the 

 Bryales, there is no real morphological distinction between 

 rhizoid and protonema. Most of the filamentous protonema! 

 branches do not remain in this condition, but become trans- 

 formed into cell plates or cylindrical cell masses, like the stem- 



FiG. 95. — A, B, Germinating spores of A. petrophila, X200; C, protonema with bud 

 (fe); D, young archegonium in optical section; E, i, 2, two views of a very young 

 embryo of A. crassinerva, X266; F, somewhat older embryo of A. petrophila; G, 

 older embryo showing the first archesporial cells; H, I, cross-sections of young 

 embryos, X200. A-D, after Kuhn; E-I, after Waldner. 



rhizoids. The flat protonema recalls strongly that of Sphag- 

 num, and is probably genetically connected with it. All of the 

 different protonemal forms, except what Kiihn calls the ''leaf- 

 like structures," vertical cell surfaces of definite form, can give 

 rise to the leafy axes. The development of these seems to cor- 

 respond exactly with that of the other Mosses, and will not be 

 further considered here. 



