DEVELOPMENT OF PLANTS 



269 



bers have a complex structure (Fig. 188). They originate in 

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



-— -fT 





Fig. 188. Section through the center of the thallus of Marchantia, show- 

 ing one of the air chambers and chimney-like pores in the epidermis — ch, 

 palisade-like chlorenchyma arising from bottom of air chamber. The lower 

 cells of the thallus are nearly colorless and filled with watery solutions or 

 mucilage, r, rhizoids; /, leaf-like plates of cells. 



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

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



Fig. 189. Diagram of a section of one of the cups shown in Fig. 186 — g, 

 buds or gemmae associated with small glandular cells. 



the chamber numerous delicate chlorophyll-bearing cells arise. 

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

 enchyma of the leaf and it is manifestly protective and adapted 

 to photosynthesis. The structure of the lower cells of the thallus 



