DIFFERENCES IN THE REACTION-INTENSITIES OF VARIOUS STARCHES. 313 



DIFFERENCES IN THE REACTION-INTENSITIES OF VARIOUS STARCHES.* 



The reaction-intensities in the case of each starch with each reagent vary within wide 

 hmits, especially in the case of the reactions with heat and chemical reagents. For pur- 

 poses of comparison these differences are expressed more satisfactorily in diagrammatic 

 form than in words and figures in the form of text. Charts A to J will be found extremely 

 instructive in showing: (1) the range of reaction-intensity of each reagent; (2) the close 

 correspondence in the case of horticultural forms, varieties of a given species, the members 

 of a genus, closely related genera, etc. ; and (3) the independence in the intensities of the 

 different reactions of a given kind of starch, for instance, when, in a given starch, the 

 temperature of gelatinization is high but the chemical reactions low, or vice versa, or when 

 the reaction with one chemical reagent may be high while with others they are low, etc. 

 These charts do not require any detailed statement as to what they show, but as an indi- 

 cator it might be desirable to suggest to the reader that the data of any arbitrarily selected 

 chart be examined in a general way. For instance, Chart D, parts 1 to 4, at a glance show 

 the wide range of the reaction, and the groupings of horticultural forms, varieties of a 

 species, members of a genus, and closely related genera. In fact, by the temperature of 

 gelatinization alone, had we more data, one might say that the starch may belong to this 

 genus or not to that genus. Thus, upon the basis of the records and limitations of this 

 research, a starch ha^'ing a temperature of gelatinization in excess of 80 might be suspected 

 to belong to Amaryllidacew, Iridacece, Zingiberacece, or Marantacece; but it would not be 

 thought to belong to GraininacecE, Aroidece, Liliacece, or other families noted. While, there- 

 fore, little weight is to be attached to the indications of the temperature of gelatinization of 

 itself as indicating the genus, yet by taking the sum of the mean reactions, the positive 

 recognition of every form of starch seems not only possible but usually exceedingly easy. 



In the case of each reagent, while the range of reaction extends from almost the lowest 

 limit of the chart to or beyond the highest limit, it will be seen that the degree of varia- 

 bility of the different starches with each agent is quite different. Thus, in the polarization 

 reactions the records range for the most part from fair to high, and in the iodine reactions 

 generally from fair to dark. The variability in the reactions with the two anilines is some- 

 what more marked, and there is a decided tendency for the records of the two charts to run 

 parallel, the gentian violet reactions being usually more marked than those with safranin. 

 In fact, eliminating the probable errors of record due to the gross standards of determining 

 the reaction, the differences in the results with these two agents might in most cases be 

 regarded as being due to differences in concentration of a given reagent. In the tempera- 

 tures of gelatinization there is, on the whole, a greater tendency to variation than in the 

 polarization and iodine reactions but less than with the anilines, and markedly less than 

 with the chemical reagents, excepting Purdy's solution, with which the reactions generally 

 tend to be towards one extreme or the other, that is, very slow or quite rapid. There 

 appears very frequently to be a manifest tendency for the grades of reaction with chloral 

 hydrate-iodine, chromic acid, pyrogallic acid and ferric chloride to correspond, so that if 

 reaction be moderate to slow with one it is apt to be the same with the others; but in this 

 respect the reactions with Purdy's solution appear to stand distinctly apart. However, 

 this is a very gross generalization, inasmuch as a starch that is very responsive to one 

 reagent may be very resistive to another, and as there are so many exceptions to the 

 generalization absolutely no rule can be formulated. In other words, the reaction-intensity 

 with each reagent must be looked upon as an independent unit which may or may not 

 have a quantitative correspondence with that of another reagent. 



* In cases where the temperatures of gelatinization exceeded the Hmits of the chart the line (ordinate) was drawn 

 to the limit; and in the chemical reactions where the ordinate is drawn to the 60-minute abscissa the reaction is in- 

 dicated as being complete or incomplete at this time, in almost all instances incomplete. 



