ERGASTIC SUBSTANCES 99 



As a result of his classic researches Nageli (1858, 1881) developed 

 the theory that the starch granule is made up of ultramicroscopic particles 

 ("micellae"), differing in size and in the thickness of their surrounding 

 water films in the various layers of the granule. He finally decided that 

 the micellae are crystalline in nature, a conclusion supported by the work 

 of Schimper (1881) with polarized light. This conception of the starch 

 granule as a spherocrystal with radially arranged elements was adopted 

 and elaborated by A. Meyer (1883, 1895), who attributed the stratifica- 

 tion of the granule to differences in the length, thickness, closeness, and 

 richness of branching of the constituent needle-shaped crystals, or 

 "trichites." The more recent X-ray analysis by Sponsler (1922, 1923) 

 indicates that the granule is made up of units regularly arranged in a 

 space lattice; it is therefore crystalline in the modern sense of the term. 

 Instead of having single atoms in planes as in an ordinary crystal, it 

 consists of CeHioOs units arranged in curved layers. 



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Fig. 51. — Carbohydrate reserves in endosperm of maize 50 days after pollination. 

 a, simple grains of starch from starchy maize, b, compound grains of starch from sweet 

 maize, c, globules of liquid dextrin from sweet maize; some of them contain simple and 

 compound starch grains. (After Lampe, 1931. Figure redrawn and furnished by that 

 author.) 



Starches vary considerably in composition and in reaction to reagents. 

 The principal constituents are a-amylose and /S-amylose, which usually 

 become reddish and bluish, respectively, with iodine. In maize endo- 

 sperm, according to Brink and Abegg (1926), the two amyloses occur in 

 different proportions in waxy and non-waxy starches; furthermore, both 

 turn red in the waxy starch and blue in the non-waxy. It may be that 

 such differences are due to variations in the degree of colloidal dispersion 

 (W. Harrison, 1911). 



In the endosperm of maize the visible reserves of carbohydrate, which 

 are deposited in plastids, are specific in form and composition in the 

 four genetic types: starchy, waxy, sweet, and waxy-sweet. In the non- 

 sweet maize simple grains of solid carbohydrate occur. They are com- 

 posed of starch in starchy maize and of red-staining "starch" in waxy 

 maize (Fig. 51, a). In the sweet types there are compound grains, which 

 are composed of starch in sweet maize and of the red-staining "starch" in 

 waxy-sweet maize (Fig. 51, h). In the sweet types globules of liquid 

 dextrin also occur in the upper central portion of the endosperm. In 

 sweet maize these globules may contain small simple and compound 



