DIRECTIONS FOR LABORATORY STUDY. 379 



6. The openings into the air chambers, in the skin over each 

 one. 



7. Compare the under surface with the upper. Observe the 

 numerous hairs. Discover the difference in place of origin and 

 direction of growth of these. (U 56.) 



8. Carefully pull off with forceps as many of these hairs as 

 possible and notice the dark-colored overlapping outgrowths 

 along the midrib, curving outward as they are followed forward, 

 attached along their edges. These are the so called "leaves." 



Cut a transverse section of the thallus through a brood-bud 

 cup. Observe 



9. The origin of the brood-buds (only the younger still remain- 

 ing) over the midrib. 



10. The difference between tissue of upper and under parts of 

 thallus. (If fresh plants are available observe especially the 

 difference in color.) 



12. Demonstration. Cut a very thin transverse section of the 

 thallus. Select a part passing through stoma and show 



(1) The air-chamber; its roof, the skin, with chimney-like 

 stoma in center; its sides a vertical plate of cells; its floor, with 

 branched filaments of chlorophyll-bearing cells. (Fig. 58.) 



(2) The large-celled colorless tissue forming the lower half of 

 section; the sections of "leaves" arising near midrib and con- 

 cave towards center. 



The sexual branches are so peculiar and specialized that the 

 beginner ought not to be puzzled with them. 



B. LEAFY LIVERWORT (Porella platyphylla). 



1. In what position do the plants grow with reference to the 

 substratum ? 



Disentangle carefully a single plant.* Observe 



2. The growing apex ; the dying base; the distinctly dorsiven- 

 tral habit. Enumerate the differences between the upper and 

 under sides, (^f 60.) 



3. The mode of branching : a central axis, with lateral 

 branches, themselves with lateral branches ; i.e., monopodial and 

 bipinnate. (IT 65.) 



4. The yellowish or brownish stem, covered with leaves 

 unequally distributed. 



* If dry, first soften by placing plants in hot water for a few minutes. 



