STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 25 



the properties of the external layer. He believes that the conditions which regulate the 

 growth of the grain by intussusception bear a very close relationship to the physical and 

 chemical jiroportics of the grains. This he sums up in the following law: The more rapid 

 the growtli in any part of the grain, the softer the substance at that point, and the more 

 readilj^ it is acted upon by swelling solvents, and since the chemical composition runs 

 l^arallel with growth, the larger will be the amount of granulose in relation to cellulose. 

 The least growth, Niigeli holds, takes place in tlie exterior part of the grain, as can be seen 

 in both simple and half-compound grains, which grains from the earliest stages do not 

 increase in thickness but grow in the same plane. While the outer layer under all circum- 

 stances is the densest and richest in cellulose content, the small young grains, unlike the 

 mature grains, consist of a dense substance throughout. In these grains there appears 

 at the center a soft hilum which is a very small point, and which increases in size and 

 density, while the surrounding substance does not change much in density. 



In a later contribution (Botanische Zeit., 1881, xl, 633) NiigeU again discusses the 

 mechanism of formation of starch-grains, and adheres to the theory of growth by intus- 

 susception. He assumes that the differentiation of the substance into lamella) is present 

 in all starch-grains, and that the homogeneous appearance of some grains is due to the 

 optical appliances not being sufficiently powerful to perceive a lamellation which may be 

 exceedingly indefinite and indistinct. That the grains are solid can be demonstrated, he 

 states, in the sprouting of starch-containing plant parts, in which the grains, like inorganic 

 crystals, dissolve from the surface inward until they disappear completely, during all 

 stages of which solution the grains are solid. The variations in the densities of the lamellie 

 he attributes to differences in the water-content. The lamellis are not of uniform thickness 

 throughout, and the inequalities he states may be distributed regularly or irregularly over 

 the entire layer. Very often two or more layers fuse into one, or one layer may split into 

 two or more. Such splitting takes place jjrincipally in the dense layers, but it may occur in 

 the more watery loose layers. A tliick lamella which on one side is simple may on the 

 other side be split into several parts of ec^ual density, between which there may appear 

 parts of less density. Complete and incomplete lamellte are arranged about a common 

 central point which sometimes is the mathematical center of the grain, but usually eccentric 

 for the entire grain and concentric only for the inner layers. The form of the individual 

 layers and the arrangement of the lamellae from the center to the periphery, in other words, 

 the structure of the grain, he states are due to the form of the hilum. In grains with a 

 lenticular hilum the short axis of the grain is in a line with the shortest diameter of the 

 hilum, which is centrally located, and the layers are usually of uniform thickness. In 

 grains with an elongated hilum, the axis of the greatest diameter of the grain is in line 

 with the greatest diameter of the liilum, wliich is central, and the layers are rather uniform. 

 In spherical grains the hilum lies at the center of the grain, and the laj^ers are always 

 circular, and have a uniform tliickiiess. All radii of such grains are equal. Another type 

 of grain is one in which the hilum is spherical and eccentrically located, and in which the 

 axis passes tlii'ough the center, on one side of which it extends through the longer radius 

 and on the other the shortest radius of the grain. Such a type is the potato starch. 



The principal forms of grains with eccentric nuclei are: (1) spherical with the hilum 

 between the center and the periphery; (2) elongated (lanceolate to conical), with uniform 

 ends or one end more attenuated, the liilum being located at either the narrower or wider 

 end; (3) wedge-shaped, elongated (1 to 3 times as long as wide), compressed on one side, 

 narrow and not compressed on the other side, where the hilum is located; (4) expanded 

 (0.66 to 2.5 as wide as long), compressed, the hilum located near the narrow end; (5) 

 irregular forms with projecting edges and angles. 



Nageli notes that in some instances lamellated grains have several hila, with as many 

 systems of lamella;. Such a grain appears as an aggregate of se\'eral lamellated part- 



