198 



PLANT MORPHOLOGY 



mature. The capsule is without an operculum, dehiscence taking place 

 by means of four longitudinal slits, but these usually do not extend to the 

 apex of the capsule (Fig. 161). 



Summary. Like the Sphagnales, the Andreaeales are a synthetic 

 group. The gametophyte begins either as a thallus, as in the Sphag- 



FiG. 161. Gametophyte of Andreaea petrophila with mature and ininiature sporophytes, 

 X3. {F rom Gilbert M. Smith.) 



nales, as a filamentous protonema, as in the Bryales, or as a cylindrical 

 body. The antheridia are terminal, as in the Bryales, but are long- 

 stalked and globular, as in the Sphagnales. The archegonia develop like 

 those of the Bryales. The sporogenous tissue is derived from the endo- 

 thecium, a feature of the Bryales, but caps the columella in a dome-like 

 manner, a feature of Sphagnum. Similarly, as in Sphagnum., a pseudo- 

 podium is developed. The capsule dehisces by means of four valves, as 

 in the Jungermanniales. 



3. Bryales 



The Bryales, or true mosses, are the culminating order of bryophytes. 

 They constitute a highly specialized, as well as a very distinct group, dis- 



