STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 37 



Meyer, in an elaborate research on starch-grains published in 1895, again takes up 

 the study of the formation and structure of the starch-grain, reference to which will be 

 found in later pages (page 47). 



Our understanding of the structure and mechanism of formation of the starch-grain 

 was added to materially by the careful observations of Strasburger (Ueber den Bau und 

 das Wachstum der Zellhflute, Jena, 1882). He states that since there is a great analogy 

 of structure between cell-membranes and starch-grains, it is natural to go from the 

 former to the latter in the study of the structure and growth, and that the large, flat, 

 eccentric starch-grains of Phaius grandiflorus {P. wallichii) are very suitable for such 

 investigations. The structure of the grains is such that the layers, except the innermost, 

 are not complete, that is, they end blindly on the side of the grain (see plate 102, fig. Gil). 

 In general, all starch-grains from the same bulb agree fully in structure and in other prop- 

 erties. When magnified, these grains show definite lamellations which are indicated by 

 broader light and narrower dark lines. The lines or lameUse may vary greatly in width. 

 Upon this alternation of light and dark lines is based the view of alternation of dense and 

 less dense layers, and of layers that are poor or rich in water. As a matter of fact, he 

 states, there are in the starch-grain, as in the cell-membrane, consecutive lamelte wliich 

 resemble each other rather closely. The darker lines are the adhesion surfaces of the 

 consecutive lamellae. Wliere these dark lines follow each other very closely they indicate 

 directly the boundaries of the lamelte; usually, however, they indicate only single adhesion 

 surfaces, and thus separate layer-complexes from each other. The more sharply marked 

 the separation-surfaces appear, the longer are the intervals between the periods of forma- 

 tion of the lamellae. The dividing lines become more pronounced by individual layers 

 becoming more dense on their outer surfaces. This accentuation, he states, may also be 

 brought about by an interruption in the growth. Small variations in the constitution of 

 the protoplasm which produce the lamellae, as a difference in the water-content, may also 

 possibly cause the variation. 



Strasburger found that by a slow action of potassium hydroxide on starch-grains the 

 grains swell. The surface was found to be the most resistant, and the outermost layer 

 was seen to be not continuous around the entire grain. The anterior and the acute end 

 of the grain was the most resistant and is the oldest part of the grain. With the beginning 

 of the action numerous fine cracks appeared on the surface, and ran with approximate 

 regularity perpendicularly to the direction of the lamellae; immediately the substance 

 between the cracks was dissolved at a number of points. The entire surface of the grain 

 was now dotted regularly, and the dots were very small and not continuous. At the same 

 time there was seen a rather large crack, which, passing out from the hilum, mantle-like, 

 inclosed the inner part of the anterior half of the grain ; it separated the denser outer part 

 from the less dense inner part; the latter escaped from the grain through openings made 

 by the rapidly dissolving posterior lamellae; the inner mass separated into two parts. The 

 dense layer and the layer-complexes do not swell as much as the less compact layers and 

 radial cracks form in them. These cracks are usually very irregular and anastomose with 

 each other. During the swelling the lines of separation between the layers and the layer- 

 complexes do not become wider, yet they become more evident. The formation of cracks 

 and their direction in the swelhng process indicate undoubtedly that a radial structure is 

 present in the grains, and leads to the conclusion that the elements of the grain are minute 

 rods arranged radially. The regularity of the cracks, Strasburger holds, opposes the view 

 that the cracks have arisen through tension in the grains. In the fresh starch-grains the 

 hilum was recognized with difficulty, but in the dried grains it was quite evident. In the 

 latter case it appeared usually to be hollow, and the fissures that crossed the lamellae at right 

 angles were directed toward the hilum. Such fissures in the dried grains extended only to 

 the concentric lamella?, and they usually terminated where the lamelte became incomplete. 



