148 SYSTEMATIC BOTANY. 



a manifest rotation of the protoplasm in the cells. The 

 sexual organs differ somewhat from those of the Carpo- 

 sporese. The "central cell," or carpogonium, is the terminal 

 one of a row of cells; from the basal cells there grow 

 upwards five elongated ones, which surround the carpo- 

 gonium, and become twisted, so as to form a spiral. The 

 antheridium is globular, enclosed by eight triangular cells, 

 called shields, which are united by zigzag margins. From 

 the centre of each shield, projects inwardly a cylindrical 

 cell, which supports many long, coiled filaments, in each 

 of whose numerous segments a long, slender, spiral, biciliate 

 spermatozoid is produced. The spermatozoids escape, when 

 ripe, by the bursting of the antheridium, and swim about 

 in the water till they find the orifice at the upper end (or 

 " crown") of the enveloping coat of the carpogonium. 

 Upon their entrance, fertilization is effected, and the en- 

 veloping Cells become hard and dark-colored. The fruit, 

 or sporocarp, falls to the bottom, where it germinates when 

 favorable conditions obtain ; and a proembryo, consisting 

 of a single row of cells, is formed, from which the sexual 

 plant is developed by the growth of a lateral bud. 



BRYOPHYTA. 



175. The Bryophyta (Mosses and Liverworts) con- 

 stitute the fifth division of the vegetable kingdom. There 

 is a well-marked alternation of sexual and non-sexual 

 generations. The first, or that proceeding from the spore, 

 bears the sexual organs, and is hence called the sexual 

 generation. After fertilization, there grows a sporocarp 

 (called sporangium), in which spores arise non-sexually ; 

 this, therefore, is the non-sexual generation. The sexual 

 organs of the Bryophyta consist of archegonia and anther- 



