196 



PLANT MORPHOLOGY 



region (the capsule), a middle region (the neck), and a basal portion (the 

 foot). As in Anthoceros, a columella is formed from the endothecium, the 

 sporogenous tissue being cut off from the amphithecium and capping the 

 columella like a dome. The sporogenous tissue becomes two to four 

 layers of cells in thickness, while the outer portion of the amphithecium 

 forms the capsule wall, eventually composed of five to seven layers of 

 cells. This becomes a region of green tissue with intercellular spaces, the 

 outer layer developing rudimentary stomata. The sporogenous tissue is 

 surrounded by a definite nutritive layer, the tapetum. As in the other 







n 



ABC D 



Fig. 160. Early stages in the development of the embryo of Sphagnum sub secundum, 

 X200. A, two-celled stage; B, four-celled stage; C, seven-celled stage; D, appearance of 

 vertical walls. {After Bryan.) 



Musci, no elaters are formed, all the sporogenous cells becoming spore 

 mother cells. 



The foot becomes large and bulbous, but the seta does not develop 

 beyond the neck-Hke stage (Fig. 158F). The seta is replaced functionally 

 by the pseudopodium, a leafless stalk developed from the stem of the 

 gametophyte, in the tip of which the foot of the sporophyte is embedded. 

 The pseudopodium elongates rapidly after the spores have ripened, carry- 

 ing the capsule upward. When mature, the capsule is globular and dark 

 brown or black. It dehisces by means of a lid or operculum, as in the 

 Bryales. The spores are discharged wdth force. As in the Hepaticae, the 

 sporophyte remains enclosed by the calyptra until the spores are ripe. 



Summary. The Sphagnales are a synthetic group, combining char- 

 acters found both in liverworts and mosses. A thallus like that of the 

 anacrogynous Jungermanniales gives rise to an erect leafy shoot that 

 becomes the mature gametophyte. This shows some internal differentia- 

 tion, both in the leaves and stem. The antheridia are spherical and axil- 



