DEVELOPMENT OF PLANTS 



255 



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 will 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. 186) is of common occurrence 



FIG. 186. 



FIG. 187. 



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

 contain buds or gemmae and also four erect branches that contain the 

 antheridia 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. 



iii 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 shows that these air cham- 

 bers 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- 

 like pore over the center of each cavity. From the bottom of 

 the chamber numerous delicate chlorophyll-bearing cells arise. 

 This arrangement of the tissues is again suggestive of the chlor- 



