104 



PLANT STRUCTURES 



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

 the herbs, 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 sporogonia of liverworts: A, Riccia, the whole 

 capsule being archesporium except the sterile wall layer ; B, Marchantia, one 

 half the capsule being sterile, the archesporium restricted to the other half; D, 

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

 central sterile tissue, the columella (cot).— After Goebel. 



(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 (Marchantia) the entire lower half 

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



