Mosses and Their Allies — Bryophytes 189 



plasts for photosynthesis. Rootlike rhizoids anchor the thallus and absorb 

 materials from the substratum (Fig. 43) . 



Marchantia is diecious, one thallus bearing male antheridia and an- 

 other thallus bearing female archegonia. On the male thallus (male 

 gametophyte) arise the stalklike antheridiophores with lohed disks at the 

 tip. The male antheridia are borne in cavities which open on the upper 

 surface of these disks. Each antheridium is an enlarged, oval structure 

 which produces coiled, bifiagellated sperms (gametes) (Fig. 43). 



On the female thallus (female gametophyte) arise the stalklike arche- 

 goniophores with small, term,inal disks bearing fingerlike rays (Fig. 43). 

 The female archegonia are borne on the undersurface of these disks. 

 Each archegonium has a hollow, tubular neck and an enlarged venter 

 with a single egg (ovum) at the base of the latter. 



The sperm swims through the water from the antheridium to the 

 venter of the archegonium where the sperm and egg fuse (fertilize) to 

 form a zygote. The latter through numerous cell divisions forms a multi- 

 cellular embryo from which develops the spore-producing sporophyte. 

 The latter consists of a foot embedded in the disk of the female gameto- 

 phyte, a seta, and a capsule (sporangium). The latter produces numer- 

 ous spores. Elongated, spiral-shaped, hygroscopic elaters {eV a ter) (Gr. 

 elater, driver) are affected by moisture and expel the spores from the 

 capsule. The spores germinate to form new male or female gameto- 

 phytes (thalli). 



There is an alternation of generations between the gamete-producing 

 gametophyte and the spore-forming sporophyte which is quite similar to 

 that in true mosses. Unlike the moss sporophyte, the Marchantia sporo- 

 phyte does not possess stomata (stom'ata) (Gr. stoma, opening) and is 

 usually smaller than in most mosses. Marchantia may also reproduce 

 asexually by the formation of special bodies known as gemmae (jem'i) 

 (L. gemma, bud) in little gemma cups or by the process of fragmentation. 



2. Porella (por -el' a) is a common leafy liverwort (Fig. 44) which 

 may form a green mass on moist soil, rocks, or rotten wood. Some 

 species of leafy liverworts may grow on tree trunks in damp forests. Some 

 species may resemble true mosses, but the liverworts are prostrate on their 

 substratum. 



Porella has three rows of leaflike structures attached to a stemlike axis. 

 The latter may be branched and is attached by rhizoids. The leaflike 

 structures are much simpler than the gametophyte of Marchantia, con- 

 sisting of one layer of cells and without a midvein. The sporophyte of 



