NUTRITION. 



169 



236. Storage. — In the higher plants storage places are 

 secured by the enlargement of roots, stems or leaves, to form 



Fig. 174.— Reserve starch. A, two cells of a potato, showing enclosed starch grains 

 The other contents not shown. B, compound starch grains from a grain of oats 

 Three of the component granules of a large grain are shown separately. C, starch 

 grains from a bean. All highly magnified. — After Kerner. 



o 



a 



reservoirs. Similar specialization of parts of lower plants 

 occurs. Carbohydrates are sometimes transformed into fats 

 for storage purposes, but carbo- 

 hydrate and proteid reserve food 

 is usually solid. Reserve car- 

 bohydrates usually occur in the 

 form of starch, sugar, cellulose, 

 gum, etc. Reserve proteids are 

 usually in the form of aleurone 

 grains. The starch is deposited in S 

 the form of large rounded or oval 

 grains (sphere-crystals), which often 



. . _ -.„ . . . Fig. 175.— Aleurone (proteid) grains. 



shOW layers Of dllierent Composition /, from seed of peony, a, from 



and density (fig. 1 74) 

 in liquid form as droplets of vari- 

 ous size, and are only rarely solid. 

 Aleurone grains are really vacuoles 

 filled with reserve proteids. Some of the proteids often 



0® 



the outer, b, from the middle, c, 

 rats OCCUr from the inner layers. //, from 

 seed of castor bean, a, in alcohol ; 

 b, after treatment with iodine solu- 

 tion and alcohol. In both, g, glo- 

 boid ; k, crystalloid. Very highly 

 magnified. — After Zimmermann. 



