30 



METHODS USED IN THE STUDY OF STARCHES. 



ent starches with each reagent, the variations in the 

 courses and degrees of separation of the two curves being, 

 on the whole, quite as significant in the differentiation 

 of the starches as differences in the percentage of total 

 starch gelatinized (see Chapter IV, page 170). In case 

 of some starches with a given reagent the percentage of 

 total starch and the percentage of grains completely gela- 

 tinized run closely together, or even almost parallel, 

 while with other starches a large percentage of the total 

 starch may be gelatinized, yet only a small percentage 

 of grains be completely gelatinized ; the same peculiarity 

 holds good in regard to any given starch with different 

 reagents. Obviously all such data must be of importance 

 in the formulation of the physico-chemical characteristics 

 of any kind of starch. In Charts F 1 to F 14 there are 

 plotted out in some percentages of macroscopic and 

 microscopic characters of plants, and in others those of 

 plant and starch characters, the abscissae and ordinates 

 being varied to meet particular and obvious conditions. 

 No one kind of chart of itself presents in full starch 

 peculiarities. In fact, a satisfactory picture of the pecu- 

 liarities of any starch can be had only by combining the 

 curves of the several kinds of charts with histological 

 peculiarities, and the polariscopical, iodine, aniline, heat, 

 and chemical qualitative reactions. In other words, 

 characters not brought out by one means of investiga- 

 tion may be by another, etc. ; hence, it is the sum-total 

 of data that must be taken in the final analysis. 



13. COMPARATIVE VALUATIONS OF THE REACTION- 

 INTENSITIES. 



Throughout all of the reactions definite standards 

 of comparison were adopted, varying somewhat with 

 the different agents, yet all forming a definite coordinate 

 system based upon common abscissae (Chart A 1, Chap- 

 ter IV). Thus, the reaction- values in the polarization, 

 iodine, gentian violet, and safranin reactions are based 

 upon a " light and color reaction " scale up to 105, from 

 to less than 20 being grouped as very low or very light, 

 20 to less than 40 as low to light, 40 to less than 60 

 as moderate, 60 to less than 80 as high or deep, and 80 to 

 105 as very high or very deep ; the terms very low, low, 



moderate, high, and very high are applied to the polariza- 

 tion reactions; and very light, light, moderate, deep, 

 and very deep to the iodine and aniline reactions, the 

 sets of terms being synonymous in so far as comparative 

 values are concerned. The reactive-values of the tem- 

 perature of gelatinization experiments range from 42 

 to 95 C. (" temperature of gelatinization " scale), 82.5 

 corresponding to 20, 72.5 to 40, 62.5 to 60, 52.5 to 

 80, and 42.5 to 100, of the foregoing scale. The 

 reaction-values of the reactions with the various chemical 

 reagents are, as previously stated, in terms of complete 

 and partial gelatinization of complete gelatinization 

 within a period of 60 minutes, and of percentage of total 

 starch gelatinized in 60 minutes, the scale consisting of 

 two parts in accordance with this division. These reac- 

 tive-values based upon the light and color scale of 105, 

 are as follows: 50 per cent of the total starch gelatinized 

 in 60 minutes corresponding to 20, and 90 per cent to 40 ; 

 complete gelatinization in 45 minutes to 60, in 25 minutes 

 to 80, and in 5 minutes to 100. 



Comparative reactive-intensities are grossly presented 

 in the text by referring the reactions to five groups upon 

 the basis of the values as they fall within the five divi- 

 sions enumerated; very low, low, moderate, high, and 

 very high. This plan has been followed in the Summaries 

 at the end of each set of parent- and hybrid-stocks, and 

 each group of sets that belong to a given genus. It was 

 found, however, in the final summing up of such data to 

 show generic differences, that the reactive-intensities 

 could better be presented when the exact value in units 

 in each reaction was taken instead of the group value. 

 For instance, two starches whose values fall within the 

 " very high " division may have very different numerical 

 values, one a value of 80 and the other of 100 or more, 

 according to the first scale given, etc. In making out 

 these values each abscissa was taken as having a value 

 of 5, making the range of the scale from to 115, the 

 abscissa having a value of 25 corresponding to 20, 45 to 

 40, 65 to 60, 85 to 80, and 105 to 100 of the " light and 

 color reaction " scale. This difference is owing to the 

 raising of the light scale 5 points higher than it should 

 have been under usual circumstances. 



