THE HRYOPIIYTA 313 



breaks open and libeiates the sperms, which swim about and 

 under favorable conditions enter archegonia and effect fcrtihza- 

 tion. Archegonia and antheridia, or structures which have been 

 derived from them, may be recognized in the gametophytes of all 

 the remaining members of the plant kingdom. 



Bryophytes are divided into two classes, the Ih'paticae and 

 the Musci. 



Hepaticae or Liverworts. — The members of this class arc low- 

 growing plants, chiefly inhabiting moist places. Their vegeta- 



0^1{^^6 



Via. 184. — Ricciocarpus, a simple, floating liverwort. The round bodies 

 lying at the bottoms of the furrows on its surface are sporophytes, each of which 

 has arisen there from a fertilized egg in an archegonium. On the lower surface of 

 the thallus are groups of thread-like absorbing organs or rhizoids. 



tive body is a flattish thallus which creeps over the surface of 

 the ground, and is attached thereto by thread-like filaments or 

 rhizoids. In some types it is cut up into leaf-like lobes. Here are 

 found the lowest and most alga-like of the bryophytes. They are 

 commonly divided into the M ar chant i ales, Jungennanniales, and 

 Anthocerotales. 



1. Marchantiales. — The thallus of these plants is a thick, 

 dichotomously forking structure, in the upper or dorsal portion 

 of which occur air spaces or chambers, communicating directly 

 with the outside and thus freely exposing to the air the delicate 

 chlorophyll-bearing cells of the interior. In Riccia and its allies 

 (Fig. 184), the simplest members of the order, the archegonia 

 and antheridia (Figs. 183 and 185) occur along grooves in the 

 upper portion of the thallus and are sunken just below its surface. 

 The sporophyte (Fig. 185) which develops from the fertilized egg 

 is nothing more than a spore case or sporangium, often called 

 among bryophytes the sporogoniuni, and here consists merely of a 

 mass of spores surrounded by a definite wall. These spores, like 

 all produced by sporophytes, occur in tetrads or groups of four. 



