22 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



intermittent growth; or (2) in many kinds of starcli both external and internal lamella- 

 tion go on independently. The latter a.ssumption he holds explains the peculiar structure 

 of starch-grains often found in Chile arrowroot (Alsirceineria), but rarely found in potato 

 starch, in which several common dense layers surround a fused group of starch-granules. 



Maschke (Jour. f. prakt. Chemie, 1854, lvi, 400), from studies of the structure of 

 wheat starch, concluded that the grains have the form of membranous vesicles, the periphe- 

 ral layer consisting of cellulose, which in starch-paste does not stain blue with iodine. 

 He heated starch in water to various temperatures. At 40 C. the grains or vesicles showed 

 large numbers of well-defined rings which are alternately hght and dark; at 60, instead 

 of intact rings, outlines of smaller grains were noticed in the center of the large grain; at 

 70 breaks and cracks were found, due to the swelling of the vesicles; and at 100 the 

 grains were rather irregular in shape, resembling collapsed bags. On the addition of 

 iodine he noted in the blue mass, granular brown-colored lumps. These phenomena can 

 be explained, he states, if one assumes that every grain is composed of from 3 to 5 vesicles 

 placed concentrically one within the other, and between them the granular amylon or 

 starch. The appearance and disappearance of so many rings he attributes to the swelling 

 and the separation of the granular amylon, ultimately leaving the 3 to 5 circles which are 

 the envelopes of as many concentrically arranged vesicles that compose the grain. He 

 believes that he has proved the existence of such an arrangement by means of the action 

 of iodine and sulphuric acid. The internal part of the starch he conceives to consist of a 

 soluble and an insoluble substance, and that by evaporation the former is converted into 

 the latter, whereas by solvents, such as lye or hot water, the reverse occurs. These two 

 modifications of starch, therefore, are believed by him to preexist in the grains. The 

 explanation of the light and dark rings, he writes, is to be found in these two modifications 

 of starch, the light rings representing the insoluble modification and the dark rings the 

 soluble modification. The hilum he describes as a central hollow of the innermost vesicle, 

 which hollow may, owing to drying, be without contents, or it may be filled with amylon 

 in solution. The insoluble starch, he assumes, is present in granules around which the 

 soluble form of starch is present in liquid form. 



The view that starch-grains grow by external accretion, and that the outer layers are 

 the youngest and last formed, received further support in the investigations of Crliger 

 (Botanische Zeitung, 1854, xii, 41) of the starch-grains in the plant-cells of Philodendron 

 grandifolkim, Dieffenbachia seguine, Batatas edulis, and other plants, the starch of Batatas 

 edulis being especially suitable for the study of compound grains. He endeavored par- 

 ticularly to determine where and how the outer layers are formed. In a number of the plants 

 examined the younger cells contained only round grains, whereas in older plants there 

 were large grains of various irregular forms, from which facts he believes that the forms 

 found in the older cells were round originally and developed into larger grains which depart 

 during growth from the spherical form because of the deposition of layers on the outside. 

 He makes the observation that all starch-grains are formed upon the protoplasmic layer 

 which lines the inner surface of the cell. The starch-grain is formed here, he holds, as 

 long as it is capable of further growth and as long as protoplasm exists in the cell. In all 

 kinds of starches with definite layers and definite eccentric hila it was seen that the liilum 

 is always located in the part of the grain farthest removed from the point of attachment 

 of the grain. When the part of the starch resting upon the protoplasm or chlorophyl was 

 examined it was found that the outside layer at this point behaved differently with iodine 

 from other parts of the grain, for while the mass became blue this outer layer tm-ned yellow 

 or dark brown, the same color as the protoplasm or chlorophyl assumes, but it did not take 

 the stain readily. This outer layer is described as being of varying thickness in different 

 starches, in some hardly perceptible ; and he regards it as a substance which is in the proc- 

 ess of becoming starch, and that it probably contains nitrogen or albuminous material. 



