VEGE TA TIVE REP ROD UCTION. 



227 



320. The sporophyte. Among the mossworts, fermvorts, 

 and seed plants reproduction by non-sexual spores has be- 

 come so fixed and important that 



one stage in the plant is devoted 

 especially to producing them. 

 This phase is different from that 

 producing sexual cells, the differ- 

 ence becoming greater the more 

 complex the plant. The stage set 

 apart for spore production is called 

 the sporophyte. In the moss- 

 worts the sporophyte has very 

 little green tissue, and therefore 

 carries on little nutritive work, 

 but depends for its supply of food 

 chiefly upon the sexual stage, with 

 which it is connected throughout 

 its entire existence (^j 68). In 

 the fernworts and seed plants, 

 however, the sporophyte possesses 

 extensive nutritive tissues, the 

 leaves, stems, and roots belonging 

 entirely to this stage. Sporangia 

 in these plants may be formed 

 either upon the stem or the leaves 

 never upon the roots. 



321. Liverworts. In the 

 liverworts the sporangium is gen- 

 erally produced at the upper end 

 of a short or long stalk. It is 

 either spherical, ovoid, or short- 

 cylindrical (figs. 64, 65). The 



spore-producing tissue occupies the greater part of the 

 interior, the wall being formed usually by a single layer of 



FIG. 229. A branch of a red sea- 

 weed \Polysif>honia o/>aca), show- 

 ing tetraspores, /, formed by an 

 internal cell of the thallus. Mag- 

 nified about joodiam. After Kiitz- 

 ing. 



