104 LABORATORY AXD FIELD EXERCISES 



3. Structure and function. 



a. Adaptations for absorption. 



(1) Observe with a hand lens the ventral surface of 



liverworts which have been freed from soil. 

 What structures do you find ? Mount and study 

 under a compound microscope. How do these 

 structures (rhizoids) differ from true roots ? What 

 other structures do you find and how are they 

 related to the plant body ? Do these structures 

 have any particular function ? 



(2) Sketch the lower surface of the liverwort, indicat- 



ing the position of the structures seen. Label 

 rhizoids and scalelike leaves. Draw more in 

 detail one or more rhizoids. 



b. Light relation and photosynthesis. 



(1) Is the general form of the liverwort thallus adapted 



for photosynthesis ? Be able to explain. Examine 

 the dorsal (upper) surface of the thallus with a 

 hand lens. Do you find anything corresponding 

 to stomata and the green mesophyll areas of leaves 

 of the higher plants? Thin surface sections 

 should be examined if difficulty is experienced 

 in determining the structure of the dorsal surface. 



(2) Sketch accurately the structure of the dorsal surface 



of the thallus as it appears under the hand lens 

 or low power. 



(3) Sections. Study sections cut vertically through the 



plant body, using low powers of the compound 

 microscope or a good dissecting microscope. Com- 

 pare the structure of the dorsal portion of the 

 liverwort with that of a green leaf. Are there 

 air spaces and an internal atmosphere ? What 

 is the disposition of green chlorophyll cells ? 



