44 OUTLINES OF PLANT LIFE. 



EXERCISE XI. 



A thallose liverwort {Marchantia polyinorfha). — Examine an entire 

 plant in water. Observe 



1. The flattened horizontal body (thallus) with central line, the mid- 

 rib, and thinner wings on each side. 



2. The notched apex (the wings outgrow the midrib somewhat). 



3. The mode of branching (forking). Examine the tips and find one 

 just branched. Do not confuse with notch of apex ; when a tip branches 

 there will soon appear two notches. Does the branch appear on the 

 side of the older thallus, or are the branches equal at first ? Are they 

 equal when older ? (If 53-) 



4. The green lens-shaped bodies (brood-buds) growing at certain spots 

 along the midrib, surrounded by an outgrowth which forms a cup-like 

 rim about the cluster. Remove a brood-bud and observe its form, 

 especially in full grown ones the two opposite notches, the growing 

 points, (t 297, fig. 177.) 



5. The air-chambers (areola) of the upper part of the thallus, showing 

 through the skin, best seen in older parts and with a lens. What is 

 their form ? Are they all alike ? (*\ 52.) 



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

 like a little pinhole. 



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. (H 51-) 



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 remaining) 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.) 



11. Demonstration. Cut a very thin transverse section of the thallus. 

 Select a part passing through stoma and show 



(i) The air-chamber ; its roof, the skin, with chimney-like stoma in 

 center ; its sides a vertical plate of cells ; its floor, with branched fila- 

 ments of chlorophyll-bearing cells. (Fig. 38.) 



