loi 



PLANT STEUCTUEES 



ous part of the higher plants. The " fern plant," and 

 the herhs, shrubs, and trees among " flowering plants " 

 correspond to the sporogonium of Bryophytes, and not to 

 the leafy branch (gametophore) or "moss plant." Conse- 

 quently the evolution of the sporogonium through the 

 Bryophytes is traced with a great deal of interest. It may 

 be outlined as follows : 



In a liverwort called Riccia the simplest sporogonium 

 is found. It is a globular capsule, without seta or foot 



Fig. 86, Diagrammatic sections of eporogonia of liverworts : A, Jiiccia, the whole 

 capsule being archesporium except the eterile wall layer ; B, Marrhanda, one 

 half the cai)sule being sterile, the archesporium restricted to the other half; D, 

 AntJioceros, archesporium still more restricted, being dome-shaped and capping a 

 central sterile tissue, the columella {col). — After Goeeel. 



(Fig. 86, A). The only sterile tissue is the single layer of 

 cells forming the wall, all the cells within the wall be- 

 longing to the archesporium. The ripe sporogonium, 

 therefore, is nothing but a thin-walled spore case. It is 

 well to note that the sporophyte thus begins as a spore 

 case, and that any additional structures that it may de- 

 velop later are secondary. 



In another liverwort {MdrrJuiiifin) the entire lower half 

 of the sporogonium is sterile, while in the upper half there 



