STAKCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 51 



dense and porous, are entirely closed. At the apex of the grains the layers are very soft, 

 but entirely closed, and the layers widen toward the base of the grain. Later, iluring 

 short periods of solution, approximately uniform layers of substance are dissolved from 

 the periphery of the grain, but the solvent action is more marked at the base, with the 

 result of opening some of the lamella? laterally. If such open layers are later surrounded 

 by newly formed closed layers, it is seen that in the periphery single open layers are located 

 between numerous closed layers. When the grain has attained its normal mature size, 

 its base is often subjected to active solution, whereby the grain becomes attenuated and 

 the layers of the base loosened. 



Meyer suggests that the dense layers are relatively rich in a-amylose, and that amylo- 

 dextrin occurs in largest quantity in the less dense, porous layers. It is, he states, possible 

 that there are starch-grains which contain only amylodextrin, or aniylodextrin and ff- 

 amylose, since not every chromatophore possesses an equally high capacity of condensation. 

 The less dense layers may be distinguished, according to Meyer, by placing the grains in 

 a solution of methyl violet and adding calcium nitrate, which causes a granular precipita- 

 tion of these layers, wliich becomes stained. Such precipitation-staining experiments were 

 carried out in exienso by Fischer (page 55). 



Referring to the causes of the variations in the forms of starch-grains in the same plant, 

 Meyer writes that the differences are due not only to the fact that the grains were not 

 formed at the same time, but also to the fact that every cell has its own biology, and that 

 even every clu-omatophore has its own individual properties. In different organs of the 

 same plant starch-grains can take on a great variety of forms. In the tubers of potato, for 

 example, the leucoplasts form mostly solitary, monarch, eccentric, conical, or oval grains, 

 with a length of 200(<, and having definite irregular layers. The polytone starch-grains 

 of a given plant part differ more from one another than the monotone grains, because in 

 them the original differences are magnified. (Further reference to Meyer's investigations 

 and his descriptions of starch-grains will be found on page 67.) 



In opposition to the view that the alternation of light and darkness is a cause, or the 

 cause, of the lamellation of the starch-grain, Fischer (Beihefte z. Botan. Centralbl., 1902, 

 XII, 227) records that when cuttings of Pellionia daveauana were kept in the dark for two 

 weeks, and then put for one week where the light of an incandescent lamp would fall on 

 them continuously, a few lamellated grains were found like those described by Meyer as 

 owing their lamellation to alterations of illumination. (See also St. Jentys, page 58.) 



Some of Meyer's conceptions and conclusions were criticized by Robert (Ber. d. 

 deutsch. botan. Gesellsch., 1897, xv, 231). According to Meyer, (3-amylose remains 

 unchanged during the conversion of raw starch into starch-paste, but Robert states that, 

 if this were true, when the temperature falls below the minimum required for forming 

 paste, the form of amylose that is insoluble in water would again assume its original con- 

 dition, which is not the case. At the temperature of gelatinization, Robert states, amylose 

 undergoes a permanent change, being converted into a substance capable of swelling to 

 a much greater degree, the nature of the change being apparently that of a hydrolytic 

 splitting of the molecule of /J-amylose into smaller molecules of similar composition, and 

 probably a further splitting into still smaller molecules at 138°, at which temperature 

 the paste is soluble in water. Robert contends that the terms a-amylose and /3-amylose 

 are not acceptable, and he proposes as substitutes farinose and granulose, respectively, 

 and he suggests that the term amylose be retained for the substance which results from 

 the gelatinization of granulose (/3-amylose) . He disagrees with Meyer's statement that 

 every grain is completely and constantly surrounded by the substance of the chromato- 

 phore, without, however, mentioning the nature of his observations. 



Salter (Jahrbiicher f. wissensch. Botanik, 1898, xxxii, 117) also followed up Meyer's 

 work, and some of Meyer's statements he confirms, but others he opposes. The following 



