BRYOPHYTA 197 



lary, as in the acrogynous Jungermanniales, but in development resemble 

 the Bryales. In position, origin, and development the archegonia show a 

 resemblance to those of the acrogynous Jungermanniales, except that, 

 when mature, the venter is massive, as in the Bryales. The general 

 organization of the sporophyte is like that of the Anthocerotales, the 

 sporogenous tissue being dome-shaped and derived from the amphithe- 

 cium; but there is no meristematic region. The seta is replaced func- 

 tionally by a pseudopodium. The capsule contains green tissue and 

 rudimentary stomata. It dehisces by an operculum, as in the Bryales. 



2. Andreaeales 



This order comprises a single genus, Andreaea, of about 125 species. 

 They are small, tufted, dark-colored mosses growing on rocks in dry situa- 

 tions, especially in cold regions. In warmer regions they are restricted to 

 high mountains. 



Gametophyte. In the germination of the spore, its protoplast pro- 

 duces inside the spore wall a mass of cells called the primary tubercle. 

 After rupturing the wall, one or more of its superficial cells give rise to 

 branching filaments. These correspond to the protonema of the Bryales. 

 Some of the filaments turn brown and function as rhizoids, while others 

 may give rise either to flat thalh or cylindrical masses. A leafy shoot is 

 then organized (Fig. 161). It may arise from the flat thallus, from 

 the cylinder, or directly from the protonema. The stem, which is pros- 

 trate, exhibits sympodial branching (like dichotomy, but with unequal 

 branches). It produces many rhizoids. The stem is without a central 

 strand, consisting of uniform, thick-walled cells. It grows by means of a 

 tetrahedral apical cell. The leaves, formed in three rows, are generally 

 without a midrib, being composed usually of thick-walled cells. 



Sex Organs. Andreaea is generally monoecious, the antheridia and 

 archegonia occurring in terminal groups on separate branches. The 

 apical cell is involved in the formation of the sex organs. In develop- 

 ment, the antheridium corresponds very closely to that of Sphagnum and 

 similarly, when mature, is long-stalked and nearly globular. The arche- 

 gonia develop as in the Bryales, the cover cell contributing to the row 

 of neck canal cells. 



Sporophyte. The first division of the fertilized egg is transverse, the 

 inner segment forming the foot and the outer segment the rest of the 

 sporophyte. A dolabrate apical cell is organized in the outer segment and 

 about a dozen cells are formed before vertical walls come in. The spo- 

 rogenous tissue is cut off from the endothecium as the outermost layer of 

 cells and caps the columella as a dome. It eventually becomes two- 

 layered. As in Sphagnmn, a pseudopodium is formed, the seta remaining 

 undeveloped. The calyptra encloses the sporophyte until it is nearly 



