Z DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



free to operate in the absence of disturbing external conditions, the histological char- 

 acteristics of the grain would doubtless be specific in relation to the peculiarities of the 

 plastid; but the conditions in the plant are ever-changing; and, as is well known, a given 

 substance being deposited in a crystalline or a non-crystalline state under varying attendant 

 conditions may take on different forms. 



The cell-sap is not only of varying composition in different plants, but also changing 

 from time to time in the same plant or cell, which factor of itself may materially modify 

 the shape of the grain. Such an influence is illustrated in the crystallization of calcium 

 oxalate, which substance may be found in a variety of forms in different plants and differ- 

 ent parts of the same plant, and modifiable by changes in conditions in the given 

 part of a plant in which the crystals arise. It may be seen as needles, rods, crypto- 

 crystalline forms, rosette aggregates, tetragonal pyramids, rhombic plates, combination 

 of pyramid and prism, combination of rhombohedron and hemipyramid, and in various 

 other forms which are stated to belong to the tetragonal or monocUnic systems. In many 

 plants the form of these crystals is quite as distinctive of the plant as the form of the starch- 

 grain, yet the differences are attributed to extraprotoplasmic conditions, and not to any 

 inherent molecular peculiarities of the substance itself. There are many instances on 

 record to show that such variations may be dependent solely upon the presence of certain 

 substances in the mother-liquor, or upon other incidental conditions: Thus, for instance, 

 in the case of sodium chloride, which under ordinary conditions crystallizes in cubes, but 

 which in the urine or in a solution of urea appears as octohedrons; or in ammonium fluo- 

 silicate which crystallizes from an aqueous solution in hexagonal forms at 6 C, in cubes 

 at 13, and in both forms at intermediate temperatures. 



Not only are starch-grains during their growth subjected to the influences of the 

 pecuUarities of composition of the cell-sap, but also to changes in temperature which may 

 amount to many degrees, and also to alterations in the plastids themselves, which are 

 ever influenced in their operations by variations in both internal and external conditions. 

 It seems, therefore, obvious that the histological peculiarities of different starches may 

 be expressive merely of variations in the conditions attending starch formation, with- 

 out in the least indicating differences in the starch molecules themselves any more than 

 differences in the forms of geometric models indicate differences in the wood of which 

 they are made. It follows, as a consequence, that if there are inlierent differences in 

 the starches of different plants, as was found in hemoglobin in relation to animals, 

 such variations must be determined by methods that are available for the differentiation 

 of isomers. 



STEREOCHEMISTRY AND SOME OF ITS APPLICATIONS. 



Modern science has brought to Ught extraordinarily important disclosures in expla- 

 nation of the differences in the properties of isomerides, and this development has resulted 

 in the formation of a new department of chemistry that is known as stereochemistry, but 

 which as yet seems to be but little understood among the rank and file of students. As 

 the laws and principles of this new science underlie the present series of investigations, 

 it seems desirable to set forth certain basic facts which wUl serve particularly to show: 

 (1) that it is theoretically possible for a complex carbon compound, such as starch or 

 hemoglobin, to exist in a countless number of stereoisomeric forms; (2) that the slightest 

 alteration in the configuration or arrangement of the component units of a molecule may 

 give rise to a change of properties that may be profound, and sometimes of a predictable 

 specific character; (3) that stereochemistry is inseparably associated with protoplasmic 

 processes, and hence with the problems of nutrition, species, disease, heredity and the 

 innumerable manifestations of protoplasmic activity which in the aggregate constitute life. 



For many years the chemical composition of substances was expressed by their molec- 

 ular forviulce, but in the course of time this was found to be inadequate to designate 



