MUSCI OR MOSSES 65 



Order i. Marchantiales, including Marchantia and Riccia. 

 Order 2. Jungennaniales, the leafy liverworts, including Porella. 

 Order 3. Anthocerotales, having the most complex sporophyte gen- 

 erations among liverworts, including Anthoceros, and Megaceros. 



SUBDIVISION II.— MUSCI OR MOSSES 



Plants found on the ground, on rocks, trees and in running water. 

 Their life histories consist of two generations, gametophyte and sporo- 

 phyte similar to the liverworts but differ from liverworts, generally, by 

 the ever-present differentiation of the gametophyte body into distinct 

 stem and simple leaves, and the formation of the sexual organs at the 

 end of an axis of a shoot. They are either monoecious, when both kinds 

 of sexual organs are borne on the same plant, or dioecious, in which case 

 the antheridia and archegonia arise on different plants. 



Order i. Sphagnales, or Bog Mosses, including the simple genus. 

 Sphagnum. Pale mosses of swampy habit whose upper extremities re- 

 peat their growth periodically while their lower portions die away grad- 

 ually and form peat, hence their frequent name of Peat Mosses. 



Order 2. Andreaeales, including the single genus Andreasa, a xero- 

 phytic habit occurring on siliceous rock. 



Order 3. Bryales, or true mosses comprising the most highly evolved 

 type of bryophytes. Ex. : Polytrichum, Funaria, Hypnum, and Minium. 



Life History of Polytrichum Commune (a Typical True Moss) 



Polytrichum commune is quite common in woods, forming a carpet-like covering 

 on the ground beneath taU tree canopies. It is dioecious, the plants being of two 

 kinds, male and female. 



Begiiming with a spore which has fallen to the damp soil, we note its beginning 

 of growth (germination) as a green filamentous body called a protonema. This 

 protonema soon becomes branched, giving rise to hair-like outgrowths from its 

 lower portion called rhizoids and lateral buds above these which grow into leafy 

 stems commonly known as " moss plants." At the tips of some of these leafy stems 

 antheridia (male sexual organs) are formed while on others archegonia (female 

 sexual organs) are formed. These organs are surrounded at the tips by delicate 

 hairy processes called paraphyses as well as leaves for protection. The antheridia 

 bear the antherozoids, the archegonia, the eggs or ova, as in the Uverworts. When 

 an abundance of moisture is present the antherozoids are liberated from the anther- 

 idia, swim through the water to an archegonium and descend the neck canal, one 

 fertilizing the egg by uniting with it. This completes the sexual or gametophyte 

 generation. The fertilized egg now undergoes division until an elongated stalk 

 bearing upon its summit a capsule is finally produced, this being known as the sporo- 

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