NUTRITION. 



1 69 



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

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



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

 The other contents not shown. A', compound starcli grains from a grain of oats 

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

 giains from a bean. All highly magnified.— After kerner. 



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 

 the form of large rounded or oval 

 grains (sphere-crystals), which often 



. . . Fig. 175.— Aleurone (proteid) grains. 



shOW layers 0\ dillcivnt composition /. from seed oi peony. ■>. to,,,, 



the outer, /'. from the middle, c, 

 and density (fig. I74). FatS OCCUr from the inner layers. //, from 



. seed of castor bean a, in alcohol ; 

 in liquid form as droplets of van- b, after treatment with iodine solu- 

 tion and alcohol. In both, f, elo- 



ous size, and are only rarely solid, boid; <■. crystalloid. Very highly 



magnified. — After Zimmermann. 



Aleurone grains are really vacuoles 



filled with reserve proteids. Some of the proteids often 



