CONSTITUENTS OF PLANTS, ETC. 



329 



Fig. 112. 



eye as if composed of par- 

 ticles of a mealy sub- 

 stance. But if we exam- 

 ine it with a powerful 

 microscope we find that 

 it is made up of grains 

 which are generally regu- 

 lar in their form. They 

 are of different forms and 

 sizes in different plants. 

 In Fig. 112 you see a rep- 

 resentation of the granules 

 of potato starch as seen 

 through the microscope. They are egg-shaped, and have 

 a covering consisting of many scales overlapping each 

 other, or perhaps consist altogether of such scales. They 

 glisten in the sun and are hard to the touch. The granules 

 of wheat starch are very 

 different; they are shown 

 in Fig. 113. They are 

 flattened and dull. The 

 granules of rice starch 

 are not rounded at all, as 

 those of wheat and pota- 

 to, but are angular, and 

 are only about one 

 twelfth of the size of 

 those of potato starch. 



We have in starch 



grains an example of a Fi s- 113 - 



body with an organized structure. The exact composition 

 of starch is not known, but is C 6 H 10 O 5 or some multiple of 

 these numbers. Probably the multiple is 3 ; if so, starch 

 is C 18 H 30 O 15 . 



