MARCHANTIA POLYMORPHA. 67 



Take a very thin slice in the same way from the lower 

 surface, and notice 



5. The shape of the cells of the epidermis, absence of 

 stomata, and the insertion of the hairs. Draw. 



Make a vertical section of the stem parallel to the 

 direction of the radiating tissues of the wings, which is 

 usually at about an angle of forty-five degrees to the line 

 of the midrib ; notice 



6. The wider colorless under part of the stem. 



7. The narrower chlorophyll -bearing upper part. 

 In the colorless portion of the stem, notice 



8. The closely packed parenchyma cells, bordered on 

 one side by the marginal row of cells forming the 

 lower epidermis. 



9. The shape of the parenchyma cells, their uniformity 

 of size, and the transverse reticulated thickenings. 



10. The smaller size of the epidermal cells, forming an 

 indefinite marginal row, the walls plain, and either 

 colorless, purple or brown. 



11. Draw several cells of the lower epidermis, and some 

 of the adjacent parenchyma. 



In the upper green layer of the stem, notice 



12. The large air cavities, from the bottom of which a 

 thick growth of (in fresh specimens very green) cells 

 arises, branching in a cactus-like manner. 



13. Note the shape of these cells, their manner of union, 

 and the rounded (in fresh specimens bright green) 

 chlorophyll grains. Draw. 



In the same section, if sufficiently thin and perfect, ex- 

 amine 



14. "^^ partition wall which separates contiguous cavities, 



