CHAPTER III. 



HISTOLOGIC PROPERTIES AND REACTIONS. 



Comparisons of the Moke Impobtant Data of 

 THE Histologic Peopbeties and the Polaei- 

 scopio. Iodine, Aniline, Tempeeatuee, and 

 Vaeious Reagent Reactions of the Staeohes 

 OF Paeent- and Hybeid-Stocks.* 

 The great volume of matter that has been recorded 

 in the laboratory investigations of the starches of 

 parents and hybrids, and which constitutes Chapter I 

 of Part II of this memoir, renders it desirable, for 

 various reasons that will be obvious, to bring together 

 in a very succinct form such of the data as seem to be 

 the more important in showing parental and hybrid re- 

 lationships and peculiarities. This has been attempted 

 in the present chapter, but the records of the histologic 

 properties in the laboratory notes are so condensed that 

 in a large number of instances the summaries in this 

 chapter will be found to be more suggestive than adequate, 

 or even have been omitted in order to avoid an almost full 

 restatement. 



In the comparisons of the properties of parents and 

 hybrids a definite system has been adopted throughout 

 all of the parent-hybrid seta. In Section 1 the histologic 

 properties and the qualitative polariscopic and iodine 

 reactions, respectively, of the parents are with rare 

 exceptions each first compared, and then those of the 

 hybrid with those of the parents, and then when there 

 are two hybrids of the same parentage their properties 

 are compared. Much attention was given in the labora- 

 tory work to the study of qualitative reactions with 

 several of the reagents, which reactions have been found 

 to be of importance not only in the study of the starches 

 of different varieties, species, and genera, but also of 

 the starches of parents and hybrids. Eeferences are 

 made to these reactions in this section, especially in 

 regard to the peculiarities of the hybrid in relation to 

 the parents. In subsequent sections the data are quanti- 

 tative, lending themselves admira;bly to both tabulation 

 and charting. 



Section 2 records comparisons of the reaction-inten- 

 sities in the polarization, iodine, gentian-violet, and tem- 

 perature experiments. The data are tabulated under 

 these headings in forms well adapted for ready com- 

 parisons, the tables being followed by brief comparative 

 summaries of the peculiarities of the reactions of the 

 parents and of the reactions of hybrid and patents, and of 

 the two hybrids when such exist. 



In Section 3 the reaction-intensities of the starches 

 expressed in terms of percentage of total starch gelati- 

 nized at definite time-intervals are tabulated under head- 



*For convenience the parent- and hybrid-stocks are usually 

 referred to briefly as parents and hybrids. 



ings that designate the reagents used, and in a form that 

 is well adapted to show parental and parental and hy- 

 brid relationships and variations in the reactions of the 

 starches with each reagent. In most of the sets of parents 

 and hybrids 31 reagents were used; in some only 5, 

 usually the same. It would have been desirable to have 

 employed the 21 reagents throughout, and also not only 

 additional reagents, but certain of the reagents in two 

 or more concentrations, but limitations of time, to- 

 gether with other conditions, rendered this practically 

 prohibitory. 



By reference to the text of Part II, Chapter I, it will 

 be seen that while making these records both the per- 

 centage of the total starch and the percentage of the 

 entire number of grains completely gelatinized were 

 recorded at the ends of the several time-intervals. As 

 will be pointed out later on (Chapter IV, page 170), 

 these two percentages vary greatly in their relationships, 

 and the differences are often of more or less diagnostic 

 importance. It was not, however, found to be desirable 

 to include these figures in the tables here given because 

 any advantage gained would be more than counter- 

 balanced by their interference with the clear-cut presen- 

 tation of the figures given, nor have they been found to 

 be of sufficient value at present to justify a separate 

 tabulation. The figures recorded in most of the tables do 

 not convey to the mind the same impressions that are 

 exhibited by charts, because they are too numerous and 

 varied; therefore, since these data are of exceptional 

 value in the determination of similarities and dissimilari- 

 ties of the starches from different plant sources they 

 have been rendered in the form of curves (Charts D 1 

 to D 691, Chapter IV, page 210), which admirably pic- 

 ture the progress of the several reactions. These charts 

 have been studied somewhat in detail, individually and 

 comparatively, in Section 4 and also in Chapter IV, 

 page 167. In these experiments records were usually 

 made at time-intervals of 5, 15, 30, 45, and 60 minutes. 

 Occasionally, when the processes of gelatinization were 

 very rapid, records were made at 1, 2, 3, 4, or 5 minute 

 intervals, and sometimes, when the processes were ex- 

 ceedingly slow, only at the end of 60 minutes. Earely 

 records were also made at 10 or 20 minutes, or other 

 periods. Little or no importance is to be attached to 

 differences in the intensities of reactions that are recorded 

 in less than 5 minutes unless the figures are quite dif- 

 ferent, small differences falling within the limits of 

 error of experiment. In the studies of the velocity- 

 reaction curves that constitute Section 4 the data per- 

 taining to the parents were first considered and then those 

 of parents and hybrids and of the hybrids, as in Sections 

 1 and 2. 



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