NON-NITROGENOUS ORGANIC CELL-CONSTITUENTS. 



113 



1. Starch, or amylum («(C 6 H 10 O s ) or C 18 H 30 O 15 ) , is almost univers- 

 ally distributed throughout the vegetable kingdom, and is the first evi- 

 dence of the decomposition of C0 2 of the atmosphere by vegetable cells 

 (G C0 2 +5 H 2 O = C 6 H 10 O 6 +12 0). It is particularly abundant in the 

 cereals, in seeds of the leguminous plants, and in the potato, and in cer- 

 tain roots, tubers, soft stems, and seeds. It forms rounded masses which 

 lie in the plasma of the plant-cells, becoming converted, in the process of 

 germination in seeds and bulbs, into soluble dextrin and sugar. Under 



Fig. 54.— Stakch-Grantjles, aftee Loebisch. 



A. pea-starch; B, rice-starch : C. oat-starch; D. wheat-starch; E. bean-starch; F. millet-starch; G, corn-starch; H, rye- 

 starch ; I, lentil-starch ; K, potato-starch ; L, buckwheat-starch ; M, barley-starch. 



microscopic examination starch appears as rounded, glistening granules 

 composed of a series of concentric rings. These granules vary in appear- 

 ance and size according to their source. In size they may vary from 

 0.004 mm. in diameter, as when found in beet-seeds, to 0.16 mm., as in 

 potato-starch (Fig. 54). 



In the following table (after Karmarsch) the diameter of the starch- 

 granules from different sources is given. Microscopic examination of 



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