Metabolism; Digestion and Translocation 257 



plasts and amyloplasts (leucoplasts), - - and the exact 

 method of formation is imperfectly understood. It is a 

 general belief that starch 

 is formed from glucose 1 

 and under the influence of 

 one or more enzymes. 

 The latter are believed to 

 be active in starch pro- 

 duction, as a rule, when 

 carbohydrates exist in the 

 cell in considerable excess 

 of use. 



Schimper considers the 

 starch grain to be a 

 spherite made up of a 

 multitude of needle-like 

 crystals radiating from 

 the center. The striated appearance commonly ex- 

 hibited seems to be due to difference in nutrition during 

 the formation, and the eccentric arrangement of the mor- 

 phological center may be due to the development of the 

 grain near the periphery of the plastid. 



Starchy products constitute a very large portion of the 

 food of man and of domestic animals, so that many prod- 

 ucts are valuable chiefly from the high starch content. 

 In passing from colder to warmer regions some of the more 

 important starch-producing plants are the following : 

 the small cereals, buckwheat, corn, beans, potatoes, sweet 

 potatoes and yams, cassava, rice, yautla, arrow-root, 



1 The view is also current that the starch molecule is split off from 

 protein material of the plastid. 



s 



FIG. 65. Starch grains of various 

 forms. 



