CELL CONTENTS 183 



In powdered leaves, stems, etc., the chlorophyll grains occur 

 in the cells as greenish, more or less structureless masses. Yet 

 cells with chlorophyll are readily distinguished from cells with 

 other cell contents. In witch-hazel leaf the chlorophyll grains 

 appear brownish in color. Powdered leaves and herbs are 

 readily distinguished from bark, wood, root, and flower powders. 



Leaves and the stems of herbs are of a bright-green color. 

 With the exception of the guard cells, the chloroplasts occur one 

 or more layers below the epidermis; but, owing to the trans- 

 lucent nature of the outer walls of these cells, the outer cells of 

 leaves and stems appear green. 



Wild cherry, sweet birch, and, in fact, most trees witn smooth 

 barks have chloroplasts in several of the outer layers of the 

 cortical parenchyma. When the thin outer bark is removed 

 from these plants, the underlying layers are 'seen to be of a 

 bright-green color. 



LEUCOPLASTIDS 



Leucoplastids, or colorless plastids, occur in the underground 

 portions of the plant; they may, when these organs in which 

 they occur are exposed to light, change to chloroplastids. 



Leucoplasts are the builders of starch grains. They take 

 the chemical substance starch and build or mould it into starch 

 grains, storage starch, or reserve starch. 



Other characteristic chromoplasts found in plants are yellow 

 and red. Yellow chromoplasts occur in carrot root and nas- 

 turtium flower petals. Red plastids occur in the ripe fruit of 

 capsicum. 



STARCH GRAINS 



The chemical substance starch (C&HioOs) is formed in chloro- 

 plasts. The starch thus formed is removed from the chloro- 

 plasts to other parts of the plant because it is the function of 

 the chloroplasts to manufacture and not to store starch. 



The starch formed by the chloroplasts is acted upon by a 

 ferment which adds one molecule of water to C 6 Hi O 5 , thus 

 forming sugar C 6 Hi 2 O 6 . This sugar is readily soluble in the 



