MOSSES. 249 



525. Order Andreaeales.* This order includes the single genus An- 

 dreaea. The plants are small but form extensive mats, growing on rocks 

 in arctic or alpine regions usually. They are sometimes found in great 

 abundance on bare, rather dry rocks on mountains. The protonema is 

 somewhat thalloid. The sporogonium opens by splitting longitudinally into 

 four valves. An elongated columella is present so that the archesporium 

 is shaped like an inverted test-tube. 



526. Order Archidiales.* This order contains the single genus Archi- 

 dium, and by some is placed as an aberrant genus in the Bryales. There 

 is no columella in the simple sporogonium. The archesporium occupies 

 all the internal part of 'the sporogonium, some cells being fertile and others 

 sterile. 



527. Order Bryales.* These include the higher mosses, and a very large 

 number of genera and species. The protonema is filamentous and branched 

 except in a few forms where it is partly thalloid as in Tetraphis (= Georgia). 

 (Tetraphis pellucida is a common moss on very rotten logs. The 

 capsule has four prominent teeth.) In a few of the lower genera (Phas- 

 cum, Pleuridium, etc.) the capsule opens irregularly, but in the larger num- 

 ber the capsule opens by a lid (operculum). A cylindrical columella is 

 present, and the archesporium is in the form of a tube open at both ends. 

 (Examples: Polytrichum, Bryum, Mnium, Hypnum, etc.) 



* As subclass in Engler and Prantl. 



