346 



BOTANY. 



450. The sexual organs are situated in depressions in 

 the upper side of the thallus, or upon the sides or ends of 

 the stems, and are surrounded by peculiarly developed leaves 

 (perielmtium) in the leaf-bearing forms. 



451. The antheridium is a more or less globular usually 

 stalked body, which arises from a single cell (hence mor- 

 phologically a trichome) by the repeated subdivision of its 

 terminal cells. Its outer wall consists of a single layer of 

 cells (0, Fig. 231, w), and its cavity is filled with a large 

 number of sperm-cells, each of which contains a single 

 spermatozoid. The sperm-cells escape by the breaking of 

 the antheridium wall, and in the water in which this always 

 takes place they rupture, and the sperm at ozoids are set free. 

 Each spermatozoid is a spirally curved slender thread of 



FIG. 234. 



Fig. 233. Development of the antheridia of Marchantia pdymorpha, in a section 

 a young antnerulial disc, r, the growing anterior margin of the disc: from r to 

 the left are shown the antheridia (a, a, a, a) in four stages of development; at an, m 

 sp, are shown the stages of development of the stomata above the air cavities be- 

 tween the antheridia. x 300. After Hofmeister 



mK^mvfaiT^ 'ongitudinal section of the apex of the thallus of Riccia glauca. or, 

 irchegonium c, germ-cell. . the unripe sporogonium, sg, surrounded by the calyp- 

 Hofmeis'ter S DeC f the arcne g ium - a ^ A X 560 ; X 300. -After 



protoplasm, provided at the anterior end with two long 

 cilia (D, Fig. 231). 



452. In some cases the antheridia are developed singly 

 upon the upper surface of the thallus, as in Riccia (Fig. 

 232). In this particular case the antheridium is deA^eloped 

 directly from an epidermal cell (A, Fig. 232, a), and so is 

 at first external,- it, however, soon becomes overarched 



