370 



OEGANOGKAPHT. 



thus a compound organism, in which a new individual, forming 

 a second generation, developed after a process of fertilization, 

 remains attached organically to its parent, from which it totally 

 differs in all anatomical and physiological characters. It is an 

 instance of alternation of generations." 



6. Hepaticace^ OB Liverworts. — The reproductive organs 

 of Liverworts are of two kinds like those of Mosses, to which 

 this order is closely allied ; they are called antheridia, and arche- 

 gonia or pistillidia, and both kinds may be found on the same 

 plant, or on different plants. 



The antheridia or male organs are variously situated in the 

 diiferent genera of this order; thiis in the leafy plants, they are 

 placed in the axil of leaves, as in some species oi Jungcrmannia ; 

 in other plants they occur in the substance of the frond or 

 thalloid expansion, as in Riccia and Fimbriaria ; and in others, 

 as in Marchaniia, they are found imbedded in the upper surface 

 of peltate or discoid-stalked receptacles {fig. 811, r). The 

 antheridia are small, generally shortly stalked, cellular sacs, of 

 an oval, globular, or somewhat flask-shaped form {fig. 812). 



Fig. 811. 



Fig. 812. 



Fig. 811. A portion of the thallns of Marchantla polymorpha, showing an 



antheridial receptacle, r, supported on a stalk, s. Fig. 812. Antheri- 



diuni of Marchaniia, discharging its small cellular contents (sperm- 

 cells). 



Their walls are usually formed of a double layer of cells, sur- 

 rounding a number of small sperm-cells in their interior. When 

 ripe the antheridium bursts and discharges its contents ; the 

 sperm-cells also burst, and each emits a single antherozoid, 

 fhytozoon, or spermatozoid, in the form of a spiral thread with 

 two or three coils, like those of Chara {fig. 817). 



The archegonia or pistillidia, hke the antheridia, are differently 



