. CHAPTER IV. 



GENERAL AND SPECIAL CONSIDERATIONS OF THE REACTION-INTENSITIES 

 OF THE STARCHES OF PARENT-STOCKS AND HYBRID-STOCKS. 



(Charts A 1 to A 26, B 1 to B 42, C 1, D 1 to D 691, E I to E 46, and F 1 to F 14. Tables B 1 and B 2.) 



The reaction-intensities of starches lend themselves 

 admirably to presentation in the form of charts, which 

 charts in turn are peculiarly well adapted for compara- 

 tive purposes. It has been found advantageous, as stated 

 in Chapter II, to render these data in three main and 

 various special forms of charts, each serving to accen- 

 tuate some special feature or features of the reactions. 

 Of the three main forms, one presents the reaction- 

 intensities of different starches with each agent and rea- 

 gent with reference especially to the specific properties 

 of each agent and reagent, and to these peculiarities with 

 reference to varietal, species, subgeneric, and generic 

 groupings ; another form exhibits in particular the prog- 

 ress of gelatinization of the starches of the parents and 

 hybrid with difEerent reagents in terms of percentage 

 of starch gelatinized; and a third form gives a com- 

 posite picture of the reaction-intensities of the starches 

 of the parents and hybrid with all or some of the agents 

 and reagents which serves in a special way to differ- 

 entiate varieties, species, subgenera, and genera, and to 

 exhibit the relations of parents and hybrids. These 

 three forms of charts are included in the present chapter 

 xmder the corresponding headings above given, and sev- 

 eral special charts have been added which later receive 

 adequate attention. The second and third forms have 

 had more or less detailed comment in the precediag 

 chapter, but additional remarks that are desirable or 

 necessary wiU follow in the second and third sections of 

 this chapter. The first form of chart will be taken up 

 for consideration in the immediately following section. 

 It has been found advantageous to present these charts in 

 two series, A 1 to A 26 and B 1 to B 42, which series are 

 complementary, but demand separate consideration. 

 The first series gives the reaction-intensities of all or 

 most of the starches, and the second series only those of 

 selected starches, the reasons for the latter being stated 

 in subsequent pages. 



1. EEACTIOlir-INTENSITIES OV StaECHES WITH EaCH 



Agent and Reagent. 



(Charts A 1 to A 26.) 



The reaction-intensities of difEerent starches with 

 different agents and reagents differ within wide ex- 

 tremes, owing in part to inherent peculiarities of the 

 starch molecules and in part to peculiarities of the 

 reagents as regards both chemical composition and con- 

 centration of solution. In some instances the starch 

 molecules alone or largely determine the reaction, while 

 in others both starch and reagent play important parts, 

 as in chemical reactions generally. Thus, as will be 

 stated fully later on, in the polarization reaction the 



starch molecule undergoes no change, the reaction being 

 physical; hence it expresses peculiarities that are in- 

 herent to the molecule. In the gentian-violet and 

 safranin reactions the organization of the molecule is 

 either unaffected or affected to an undetectable degree, 

 the reactions being presumably adsorption phenomena. 

 In the iodine reaction there is probably a combination 

 of the iodine and starch, but without apparent inter- 

 molecuJar disorganization. In the temperature and 

 chemical-reagent reactions there is an intermolecular 

 breaking dovm by a process of hydration, with which 

 process there may be associated reactions that vary in 

 character in accordance with peculiarities of the com- 

 position of the reagents. If the molecules of the starches 

 from different sources are in the form of stereoisomers it 

 follows, as a corollary, that they must act differently 

 with different agents and reagents and that, inasmuch 

 as the agents and reagents differ, each starch should 

 show differences that are related to variation in the kind 

 of agent and in the composition and concentration of 

 the reagents. In other words, the reaction in each case 

 is conditioned by the kind of starch and the kind of 

 agent or reagent. Such is in fact what has been found 

 experimentally, as the subsequent data show. 



The most conspicuous features of these charts may 

 be summed up as follows, consideration in detail being 

 given under the corresponding headings : 



The wide range of reaction-intensities, the extent of 

 which varying with the different agents and rea- 

 gents, and being most marked with the reagents. 



The manifest tendency to groupiag of the reaction-iuten- 

 sities of different starches in harmony in general 

 with botanical groupings. 



The individuality or specificity of each chart that is 

 definitely related to the character of the agent or 

 reagent, this characteristic being most obvious in 

 the reactions in which the starch molecule is dis- 

 organized. 



The specificities of the components of the reagents that 

 are accountable for variations in the reaction-inten- 

 sities and in the qualitative changes apart from those 

 dependent upon differences in stereoisomerie forms 

 of starch. 



The variable relationships of the reaction-intensities in 

 the different charts as regards sameness, intermedi- 

 ateness, excess and deficit of reactions of the hybrid 

 starch in comparison with the parental starches. 



Variations in the reaction-intensities of the starches as 

 regards height, sum, and average. 



The average temperatures of gelatinization compared 

 with the average reaction-intensities. 



139 



