THE INTERNAL STRUCTURES OF PLANTS. 



209 



maturity, various substances are found within them, 

 of different kinds and amounts in different species of 

 plants. 



Look at a section of potato under the micro- 

 scope, and observe the minute grains within the cells. 

 Compare your specimen with Fig. 379. Fig. 380 

 represents some of the cells more highly magnified. 



FIG. 879. 



FIG. 380. 



EXPERIMENT. Place upon the freshly-cut surface 

 of potato, apple, or almost any fresh vegetable, a 

 drop of tincture of iodine. These starch-granules will 

 be colored violet, indigo-blue, or 

 deep-blackish blue, depending up- 

 on the strength of the solution 

 used. If there are albuminous 

 granules in the cell, they will be 

 colored brown or yellow by the 

 iodine. By this means the con- 

 tents of the cell are made more 

 distinct, and the cell-wall is ren- 

 dered more obvious. 



Starch-grains are either irregular, spheroidal, or 

 egg-shaped bodies (Fig. 380), having their surfaces 

 marked with concentric circles around points. These 



