CHAPTER XVI. 



THE PLANT WORLD CONTINUED 



THE THREE HIGHER GROUPINGS 

 BRYOPHYTES 



Bryophytes are usually said to possess archegonia ( ; 



or primitive egg gonads composed of many cells as contradistinguished 

 from the thallophytes which, when they possess gonads at all, are prac- 

 tically always composed of single cells. 



Bryophytes are moss-plants and liver worts, and their life-cycle con- 

 sists of two stages, the sexual and the sexless. When these stages follow 

 each other it is called an "alternation of generations." The sexual plant 

 or gametophyte forms eggs and sperm which unite, while the asexual 

 plant or sporophyte is the plant which grows from the fertilized egg of 

 the sexual plant. This non-sexual plant forms asexual spores which in 

 turn grow into gametophytes. 



Bryophytes may be quite simple resembling the thallophytes, or 

 form a leafy stem as in the mosses. 



There are some 12,000 different species of mosses or Musci, as they 

 are technically known. These are divided into three distinct orders : 



1. Sphagnales ( ). The peat-mosses. (Fig-. 



107.) 



Fig. 107. 



The Peat Moss, 



Sphagnum. 



Fig. 108. Andreaea Petrophila. 

 A, plant with mature sporophyte. 

 B, longitudinal section of sporophyte. 

 Ps, pseudopodium ; col, columella. 

 (From D. H. Campbell's "A University 

 Text-Book of Botany," by permission 

 of The Macmillan Co., Publishers.) 



