STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 45 



The softer layers, he observes, are present in much larger numbers than the denser layers. 

 Very often a grain shows only 4 or 5 dense layers, while between them are numerous soft 

 layers. The lamella; are separated from each other by dark lines which Binz holds must 

 be regarded as very tliin layers, for it is evident, he states, that when two substances of 

 different rcfractivity are in contact a boundary line must result. 



Binz holds that Niigeli's view that layers arise by the splitting of layers already 

 present, is not justified, and that the correct view is that formulated by Schimper, which 

 is that the starch-builder deposits the layers. Whether the lamella? are deposited directly 

 or whether they are secondary phenomena Binz could not determine; nor was lamellation 

 found to be attributable to the action of ferments, as Meyer assumed. 



Binz discusses various other topics, such as the relations between the structure of the 

 chloroplast and the form of the starch-grain; irregular starch-grains, compound and half- 

 compound grains; solution phenomena of starch-grains; and the structure of chloroplasts. 



The main conclusions of Binz's researches, briefly stated, are: (1) Niigeli's theory 

 that layers arise by the splitting of other layers does not hold good for the starch-grains 

 of Pellionia. (2) The outer layer of the starch-grain is the youngest, and the innermost 

 the oldest. (3) The spherical part of the grain forms when the grain is within the chlo- 

 roplast, complete layers being formed so long as the grain is entirely within the chloro- 

 plast and the wedge-shaped incomplete layers being formed after the grain has broken 

 through the builder, so that the form of the starch-grain is directly related to the form 

 of the chloroplast. (4) The extruded grain grows at the point at which it is attached to 

 the chloroplast. (5) Outgrowths and secondary growths are sharply defined from the 

 original starch-grain. (6) If the chloroplast becomes detached from a certain part of the 

 grain, the growth of the grain ceases at that part. (7) Compound and half-compound 

 grains do not originate by division of the original simple grain, but by the formation of 

 several starch-forming centers in a chloroplast. The compound grains may also originate 

 by the grouping together of several starch-builders, as seen in the pith of Philodendron and 

 Convallaria stanhopea. All these points, he writes, favor the apposition theory of growth, 

 but the theory can not be proved definitely until the origin of the lamellaj is better under- 

 stood. (8) The structure of the starch-grain has no influence upon the manner of corro- 

 sion, but upon the intensity of it, for the softer parts are more easily corroded than the 

 denser, and the several layers are more easily corroded in a radial than in a tangential 

 direction. (9) The chloroplast consists of a homogeneous ground-mass, or stroma, with 

 embedded pigment spheres, the grana. (10) Starch-builders in the form of leucoplasts are 

 present in the growing tips and they are structures homologous to the chloroplasts, since 

 under the influence of light they are transformed into chloroplasts. 



The microscopic structure of the starch-grain was studied by Biitschli (Botanisches 

 Centralblat, 1893, lvi, 150), who found that starch-paste of medium density, on drying, 

 first assumed a honey-comb structure and subsequently a fibrous form. In gelatinous 

 paste, and in a dilute solution of starch that is frozen, the same characteristic honey- 

 combed appearance was noted. From these results he concluded that the lamellation 

 of starch-grains bears a close relationship to a honey-combed structure. 



Examinations of starch-grains in water were found by Biitschli to indicate that there 

 are traces of a honey-comb structure in the inner layers and also in the hihun, but that 

 such observations did not furnish definite results. When grains of a form of commercial 

 arrowroot (canna starch) were heated in water at 60° to 70° C. until they began to form a 

 paste, it was seen that every layer of the grains is radially striated, and that eveiy layer 

 is composed of "honey-combs" whose walls consist of firm starch-substance, and whose 

 contents are water or dissolved starch-substance. These radial structures, Biitschli states, 

 do not extend through the entire grain, but alternate with each other in successive layers. 

 This structure was seen in slightly swollen starch, but not when much swollen, because in 



