A MANUAL OK BOTANY 131 



plant. Examine carefully the lighter areas. If possible, 

 discover the cell network making up the surface. 



A higher magnifying power will reveal the small green 

 ddoroplasts in the cells. Compare for form and size the 

 cells near the margin with those near the center of the axis. 

 What is formed by the latter? Similar features were ob- 

 served in fu(;us. 



Study a section of the axis Qp) and observe the cell struc- 

 ture and air chiunbors. Explain how the plant floats. 



Drawings. Show all the features of plant structure, by 

 pro])cr drawings. 



Questions. How does the plant body of the riccia differ 

 from most of the alga3 studied ? What effect has the flat- 

 tened condition on the ability to float? Some of the red sea- 

 weeds have a flattened thallus ^ plant body, but they arc the 

 exception in algae. After a study of the next subject observe 

 the gradual change from the alga3 to the land liverworts 

 shown by this plant. How is this plant fitted for life on the 

 surface of still waters ? 



Type 2. A Land Liverwort ^ 



Habitat. Marchantia is a very common i)lant in nearly 

 all regions, growing in deep shade where there is abundant 

 moisture and more or less bare earth or rock. It seems to 

 favor particularly earth that has been burnt over. It is 

 found commonly in greenhouses (being considered an evi- 

 dence of poor management). It can be grown in a Wardian 

 case in the laboratory. Lunularia and coiiocejJuihis, some- 

 what similar species, are occasionally found in quantity in 

 somewhat similar situations. If possible, examine these 

 plants wdiere they grow, or placed in dishes in a natural 

 position. With reference to the earth's surface, are tliey erect 



1 A tlialhis is a i)laiit liaviiii,' no distinction of su-ni ami loaf. 



2 Alarchantia. 



