VEGETA TIJ'E REPROD UCTIOX. 



227 



320. The sporophyte. — Among the niossworts, feinworts, 

 and seed jilants 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 diflerent 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, ^yith 

 which it is connected throughout 

 its entire existence (^ 68). In 

 the fernworts and seed plants, 

 however, the sporophyte i)Ossesses 

 extensive nutriti\'e 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 

 li\-erworts the sp)orangium is gen- 

 erally produced at the upper end 

 of a short or long stalk. It is 

 either spherical, o\'oid, 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 



P^iG. 229. — \ brancli of a red sea- 

 \s eed ( l\Tlysi/'hi>iua <^/'iZi\t), show- 

 ing tctraspores, /, formed bv an 

 internal cell of tlie thallus. ^Iag- 

 nified about loodiam. — .\fterRiJtz 



