4 OVl'LINES OF PLANT LIFE. 



grains (fig. 3). In other cells, particularly in highly colored 

 parts, the plastids may become of most diverse form and 



size, and take on a red or yellow 



color (fig. 4). 



7. Wall. — The cell-wall is 



-z 

 ...0 



D^* 



Fig. 2. Fig. 3. 



Fig. 2. — A cell from the interior of the leaf of the oat, showing its wall, and some 

 inclusions of the protoplasm, z, the nucleus ; c, chloroplasts ; o, an oil-drop. Mag- 

 nified about 1000 diam. — After Zimmermann. 



Fig. 3. — Part of the cell contents of an inner cell of white potato, z, nucleus ; j, starch 

 grains, each having been formed by a leucoplast, /, which is still attached to one side 

 of the grain ; A, crystalloid. Magnified about 1000 diam.— After Zimmermann. 



formed by the protoplasm. In green plants when first 

 formed it consists chiefly of cellulose^ with which, as it grows 

 older, various other substances may be mixed. Some of these 



A B c 



Fig. 4. — A, chromoplasts from flower leaves of an orchid \ B, from the root of carrot ; 

 C, from the fruit of mountain-ash. Embedded in the protoplasmic body of the 

 chromoplast are sometimes proteid crystalloids, /, pigment-crystals, J", or starch- 

 grains, s. Magnified about 1000 diam — ^After Schimper. 



are present even in the young wall, and may increase with 

 age ; others are characteristic of special changes which the 

 wall may undergo. 



