Mosses and Lichens 



Section of plant. (i) Shows well-marked epidermis. 



(2) Shows that each pore leads into an air-chamber. 



(3) That the side walls of each air-chamber support the 

 epidermis as a roof. 



(4) That cells containing chlorophyll spring up from the floor 

 of each chamber. These cells assimilate gases which enter the 

 air-chamber through the pores, they also take in oxygen gas and 

 give out carbon-dioxide gas. The floor-cells transmit or store 

 up food. 



CCiU. 



Marchantia polymorpha. Vertical section through the thallus at a point 



where a pore occurs. 



Habit of flowering. Antheridia or male organs are imbedded 

 in the upper surface of a shield-shaped, radially lobed disk sup- 

 ported by a peduncle and bearing scales on the 

 under surface. This male receptacle (androecium) 

 grows from the upper surface of the thallus. 

 Archegonia or female organs are borne on the 

 under side of a radially lobed disk supported 

 upon a peduncle on the upper surface of the 

 thallus. The lobes are finger-like, 8 to n, usually 

 curved downward. 



Section of male disk. Shows antheridia con- 

 cealed in depressions in the surface of the disk. 



Male flowers (antheridia). Oval upon a pedi- 

 cel (seta). Section shows a wall and numerous 

 cells containing spermatozoids, each with two 

 fine cilia. 



Section of female disk. Shows archegonia on the under 

 side of the disk. 



96 



Marchantia 

 polymorpha. In 

 ascending order 

 the cuts show 

 stages in the de- 

 velopment of an 

 antheridium. 



