34 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



Vines (The Physiology of Plants, 1886) assumes a difference in the functions of chlo- 

 roph}'l corpuscles and leucoplasts in that in the former the synthetic processes begin with 

 such simple substances as CO2, water, and salts, and are effected under the influence of 

 light, whereas in the latter they begin with tolerably complex substances, such as asparagin 

 and glucose, light not being essential. 



The contention of Schimper that starch-grains are formed by apposition brought 

 forth another contribution by C. NageU (Botanische Zeit., 1882, xl, 633) in defense of the 

 intussusception theory. Nageli writes that he was led to the adoption of the intussuscep- 

 tion theory because in the originally dense grain there appears a soft hilum, and that 

 later, when the dense layers have attained a certain thickness, there is inserted a soft 

 layer. He assumes that the starch-grain is composed of very small invisible particles 

 (which he here refers to as micellce) which have a crystalline character and grow as crystals 

 do, and which attract water to their surfaces. If unilateral pressure is applied to the grains, 

 tangential as well as radial cracks form. The cohesion of the grain he holds is less in the 

 radial than in the tangential direction, on account of the alternate dense and soft layers; 

 and the cohesion of the single layers is also greater in the radial direction. For various 

 reasons it seemed to Nageli that the soft layers possess a gelatinous, brittle consistencj-, 

 and are not semifluid, and therefore that cracks might occur in these layers, which would 

 not be the case were they semifluid. Stains and solvents in small quantities, he states, 

 penetrate the starch-substance and are deposited in varying proportions. Such deposition 

 is dependent on two causes: on the relation of the stain and the solvent to the starch and 

 the peculiar micellar constitution of the starch-substance, and on the dynamic action 

 which is conditioned by the constitution of the starch-substance. The molecules of the 

 stain he conceives to remain dissolved in the imbibitional liquid, or extracted from it and 

 deposited in the starch micellae. That different stains behave differently is shown by the 

 dissimilar relations of starch-grains toward the same stain in different solvents, and by 

 their relation towards different stains in the same solvent. Starch-grains in their natural 

 condition, he found, may not take stain, while the swollen grains take an intense stain. This 

 he explains upon the assumption that unchanged starch substance offers a greater resist- 

 ance to the deposition of stains because of the regular and compact arrangement of the 

 micellse. In the swollen, disorganized starch substance the micellae are disarranged, and 

 therefore lack the power of resistance against foreign molecules. 



Nageli believes that the softer parts of starch can not be regarded as a paste-like 

 substance disorganized by swelling, because the cohesiveness of the grain prevents such 

 a disorganization. Tension in the starch-grain which surpasses the limit of elasticity 

 brings about a rendering of the substance, but not a swelling. In grains dried and again 

 moistened, cracks were found evident only in the unchanged starch-substance. By slow 

 action of artificial swelling agents, cracks appear, and disorganization takes place in pro- 

 portion to the strength of the disorganizing medium. He holds that if the negative tensions 

 which result from the growth-processes within the grains are to be explained satisfactorily 

 by the storing of water (as Schimper believes), and not by a storing of starch-substance 

 according to the intussusception theory, the formation of the soft center or hilum and the 

 softer laj^ers can not be accounted for, and by such an explanation the interior of the grain 

 must be disrupted by cracks. 



Nageli also attacks Schimper's view that water is stored more abundantly parallel 

 than perpendicular to the lamellae, and that on this account different conditions of tension 

 are caused. He contends that the starch-grain at every stage of its growth is surrounded 

 by a watery liquid, by an intermicellar w^ater-containing system, whose tensions are always 

 at an equUibrium. When the grain is dried cracks are formed, which shows that the equi- 

 librium is disturbed by drying; and the cracks have a radial direction, crossing the layers 

 at right angles, which is proof that more water is lost in a tangential rather than in the 



