282 STRUCTURE OF MARCHANTIA 



of cells and the spore mother cells will not appear until late in its 

 growth and they will be confined to definite regions and only con- 

 stitute a small part of it. We now call the gametophyte the plant 

 because it is many times larger than the sporophyte, but we shall 

 see the sporophyte become quite as conspicuous as the gameto- 

 phyte, as in the mosses, and finally it will become much larger, 

 as in the ferns. Then we shall call the sporophyte the plant. 



(/) Structure and Life History of Marchantia.- — Let us now 

 examine a higher type of the Marchantiales, as Marchantia, and 

 note the advances that have been made over simple forms like 

 Ricciocarpus. Marchantia (Fig. i86) is of common occurrence 



i ^ 



1| '«% 





0mi& 



Fig. 1 86. Fig. 187. 



Fig. 186. Thallus of Marchantia bearing three cup-like organs that con- 

 tain buds or gemmae and also four erect branches that contain the anther- 

 idia in their upper surfaces in radiating lines. 



Fig. 187. Portion of the surface of the thallus of Marchantia enlarged, 

 showing the rhomboidal air chambers and air pores. 



in moist places, often appearing in greenhouses on the earth of 

 flower pots, and it also forms luxuriant beds on the damp ground, 

 especially where logs and brush have been burnt. The thallus 

 shows the same general features that we have noticed in Riccio- 

 carpus, being rather fleshy and creeping over the ground, to which 

 it is attached by numerous rhizoids. The simple air chambers 

 noted in Ricciocarpus are much enlarged and appear as diamond- 

 shaped or rhomboidal plates on the surface of the thallus (Fig. 

 187). Thin sections across the thallus show that these air 

 chambers have a complex structure (Fig. 188). They originate 

 in the upper cells of the thallus and as they enlarge they become 

 covered by a well-developed epidermis which forms a chimney- 



