30 LABORATORY AND FIELD EXERCISES 



PLASTIDS IN PLANT CELLS 



CHLOROPLASTIDS IN CELLS OF ELODEA CANADENSIS 

 (WATER WEED) 



1. Mount in water young leaves of Elodea selected from 

 the apex of Elodea plants, and observe as follows : 



a. Cellular structure of the Elodea leaf. 



(1) What is the nature of the cells which compose the 



Elodea leaf ? Are they uniform in size and shape ? 

 What is the color of the cell walls ? What is the 

 nature of the cell contents ? 



(2) Draw ,an outline diagram of the Elodea leaf. Indi- 



cate, by lines or by shading, the main cell areas 

 of the leaf. Fill in three or four cells of each area 

 to show the cell structure of the leaf. 



b. Chloroplastids. Observe the form and appearance of 



the green grains, or plastids, in the ElodeaAe&i cells. 

 Do these plastids occupy the same position in all 

 the cells'? Is there any regular or uniform position 

 assumed by the plastids ? 



c. Protoplasmic streaming. This is usually best observed 



in the elongated cells composing a central strand, 

 or midrib, in each leaf. 



(1) Observe this streaming movement. Is there one 



direction for the movement of protoplasm in 

 different cells in Elodea ? Does the protoplasm 

 stream from cell to cell through the cell wall ? 

 Do these cells have a cytoplasmic sac ? 



(2) Draw two or three cells of Elodea accurately, indi- 



cating the form and position of the plastids. Indi- 

 cate directions of movement by means of arrows. 

 Draw two or three plastids greatly magnified. 



