CHAPTER I. THE CELL. 



135 



up and lose their angles when treated with a solution of potassium 

 hydrate. They are stained yellowish brown by iodine and exhibit 

 the other reactions of proteid matter. Although often enclosed 

 in aleurone grains, they also occur independently in tubers and 

 thickened roots, as well as in seeds. 



Carbohydrates. These are complex substances containing 

 carbon, to which are united hydrogen and oxygen in the same 

 proportion as that in which they occur in the water molecule. 

 Among the most important of this class of cell contents is starch. 

 Its chemical composition is either C 6 Hi O 5 , or some multiple of 

 this. It is, therefore, either isomeric or polymeric with cellulose. 

 Its first formation, as has been stated, is due to the action of 



Fig. 377. 



Fig. 378. 



Fig. 377.- Starch grains from the potato tuber. Magnified about 200 diameters. 

 Fig. 378. -Wheat starch. Magnified about 500 diameters. 



chlorophyll under the influence of sunlight, and it is temporarily 

 deposited in the form of minute granules in the chlorophyll- 

 bodies ; but it subsequently undergoes solution, and that which 

 is not immediately required in the formation of tissues is stored 

 in various parts of the plant as a reserve food material. Thick- 

 ened roots, tubers and seeds commonly contain it in abundance, 

 but it also frequently occurs in the pith, medullary rays, and 

 various other parts of the plant. It is seen in the form of hard 

 granules of various sizes which often possess shapes and mark- 

 ings so characteristic that they may serve for the identification 

 of the plant. In some cases the granules are simple ; in others 

 they are compound or aggregated into masses. The starches of 

 the Potato, Wheat, Maranta and Curcuma afford examples of the 

 former, while those of Oats furnish illustrations of the latter, 

 Figs- 377, 378. y,9, 3 8o > 3 Sl - 



