812 THE BIOLOGY OF THE PLANT 



by a rather thick mass of large, clear cells, some 

 of which contain brown oil globules. Notice 

 also the rhizoids. 

 Make a diagram showing the position of all these 



parts. Put on the high power and study these parts 



separately. 



Of how many layers of cells does the " epider- 

 mis" consist? What is their shape as seen side- 

 wise ? Do they contain chlorophyll ? What is 

 their arrangement at a stoma ? Notice that air- 

 bubbles are frequently present in the tissues, es- 

 pecially under the stomata. What is the shape 

 of the cells in the green band ? Are they closely 

 or loosely packed together? Is their green color 

 due to the fact that their chlorophyll bodies are 

 larger or that they are more numerous than else- 

 where in the plant? Can you give any reasons 

 for the presence of this band of cells in this par- 

 ticular portion of the thallus ? Are any of these 

 cells apparently branched ? 



Examine the nearly colorless cells making up 

 the greater part of the section. What is their 

 shape ? Do you find them so arranged as to 

 leave many intercellular spaces ? What do these 

 cells contain ? What portion of the midrib do 

 they form ? Do any of these cells show pit-like 

 markings in their walls ? 



h. The rhizoids. — With the fine forceps tear off a 

 bunch of rhizoids. How many kinds do you find ? 

 How do you distinguish them? What is their 

 structure? Examine your sections for rhizoids. 

 From what cells in the thallus do they grow? 

 What do the rhizoids contain ? 



