12 PEOTOPLASM AND PLANT CELLS 



20. Leucoplasts are colorless plastids occurring in the 

 parts of the plant not exposed to light. When exposed 

 to light they usually produce chlorophyll and become 

 green, showing that they are essentially the same as the 

 chloroplasts. They are abundant in parts of the plant 

 where starch is being stored up. 



21. Chromoplasts are found in the cells of many 

 flowers and fruits and other colored parts of plants. 

 They are small, round or angular or needle shaped 

 plastids, mostly red or yellow in color. They contain 

 carotin or other coloring matters but no chlorophyll. 

 In many cases they are directly developed from chloro- 

 plasts by the loss of chlorophyll and the development of 

 some other pigment. 



Laboratory Studies. — (a) Mount a leaf of moss and examine 

 for chloroplasts. 



(6) Soak a few moss leaves in strong alcohol for twenty-four 

 hours and note the decoloration of the chloroplasts. 



(c) Examine Spirogyra for spiral, ribbon-shaped, or Zygnema 

 for star-shaped chloroplasts. 



(d) Soak a handful of leaves in alcohol for several hours. If 

 the flask containing the alcohol and leaves be placed in hot 

 water the extraction of the chlorophyll will progress more 

 rapidly. Note the green color of the extract. Add a little 

 gasoline or benzine (not benzene, i.e. benzol) to the alcoholic 

 solution and shake thoroughly and then let it stand until the 

 alcohol and gasoline separate. The chlorophyll will be found 

 now in the gasoline, the carotin remaining in the alcohol. 



(e) Examine the cells of various fungi, e.g. toadstools, 

 puffballs, molds, etc., or of a parasitic flowering plant, e.g. 

 dodder (Cusouta), and note the absence of chloroplasts. 



(/) Sprout a potato in darkness. Make a section of its stem 

 and compare with a similar section of the stem of a potato 

 grown in light. Note the leucoplasts in the former and the 

 chloroplasts in the latter. Similarly compare the stomatal 

 guard cells of the epidermis of green and blanched celery. 



{g) Examine the cells of a carrot root for chromoplasts 



