22 



INTRODUCTION. 



serves to characterize any part or property of starch or 

 plant. Inasmuch as each such property is a unit of com- 

 parison, each may appropriately and advantageously be 

 referred to as a unit-character. A unit-character such 

 as the property of gelatinizability may be manifested in 

 varied phases or modified forms which conformably are 

 distinguished as unit-character-phases. .Many of the 

 unii>-characters and unit-character-phases that have been 

 studied in this memoir may seem to be unimportant or 

 even trivial, but experience in various lines of inquiry 

 has shown that the correlation of such properties may 

 prove of the greatest importance. 



Each property of starch, whether it be manifested 

 by peculiarities of form, hilum, lamellae, or size of the 

 grains, or in the reactions in polarized light, or in the 

 reactions with iodine or the anilines, or in the gelatiniza- 

 tion reactions with heat and the various chemical rea- 

 gents, is an expression of a physico-chemical unit-charac- 

 ter that is one of many indexes of the peculiarities of 

 intramolecular structure of starch, and is an independent 

 unit although correlatively related to the others. These 

 unit-characters fall into arbitrary but natural groups in 

 accordance with the methods of investigation employed, 

 and as a matter of convenience and facility of study they 

 have been treated under the designations above noted. 

 Under the designation form are included a number of 

 unit-characters which are expressed specifically in the 

 occurrence of varieties or types of the grains (whether 

 as isolated, aggregates, or compound grains), their 

 numerical proportions and the peculiarities of the com- 

 ponents in number and arrangement of the aggregates 

 and compound grains; the regularity of outline of the 

 grains, and the kinds and causes of irregularities ;. the 

 conspicuous forms, etc. Under the designation hilum, are 

 included characters that are specifically expressed in dis- 

 tinctness, form, number, fissuration, and eccentricity. 

 Under lamellm are designated properties specifically ex- 

 pressed in distinctness, form, fineness or coarseness, 

 variety and distribution, and number. Under size are in- 

 cluded the ratios of length to breadth, general dimen- 

 sions of grains of different types, especially of those of 

 common size. Under polariscopic properties are charac- 

 ters that are expressed by peculiarities of the figure or 

 " cross " in regard to eccentricity, distinctness, definition, 

 courses, and other characters of the lines ; the occurrence 

 of single or multiple figures, the degree of polarization ; 

 the appearances with selenite of the quadrants as regards 

 especially definition, equality of size, form, and colors. 

 Under iodine reactions are included character reactions 

 of the raw starch grains; and after boiling the grains, 

 the reactions of the grains, solution, grain-residues, and 

 capsules. Under aniline reactions are included charac- 

 ters elicited hy the degree of staining by gentian violet 

 and safranin immediately and after a half hour. Under 

 temperature reactions are included the temperatures of 

 gelatinization of a majority of the grains and of all 

 or practically all of the grains. Under voA-ious reagents 

 are included character manifestations thait are expressed 

 hv Quantitative and qualitative reactions with various 



gelatinizing reagents. With each reagent it is found 

 that there are peculiarities in respect to the percentages 

 of the entire number of grains and total starch gelatin- 

 ized at definite time-intervals; and to the number and 

 kinds of gelatinization processes, these processes varying 

 in both particulars not only in different starches with the 

 same reagent, but also in the same starch with different 

 reagents. Hence, while the property of gelatinizability 

 is a fundamental or primary unit-character, it may be 

 manifested iu as many phases or modifications {unit- 

 character-phases) as there are starches and gelatinizing 

 agents. Among all of the varied properties of starches 

 there seems to be none so certain to show slight intra- 

 molecular differences as these unit-character-phases. 



The independence of each of these unit-characters 

 and unit-character-phases of each other will be found 

 to be well exhibited in every one of the groups of proper- 

 ties comprised in the several foregoing designations. 

 This is most strikingly shown in hybrids — ^for instance, 

 in the general characters of the hilum the properties 

 of the hybrid may be identical with those of one parent, 

 while in eccentricity identical with those of the other 

 parent, or intermediate, etc.; in the qualitative reac- 

 tions with chloral hydrate some of the processes of gela- 

 tinization may be more like or identical with those of one 

 parent; others, more like or identical with those of the 

 other parent; others, which are individual are therefore 

 not observed in either parent, etc. Hence, it is found, 

 in summing up the imit-characters and unit-character- 

 phases, that certain of the characters embraced in any 

 designation may tend in one parental direction while 

 others tend in another, but usually it is found that in 

 the aggregate there is a variable degree of leaning to one 

 or the other parent. Moreover, while such group proper- 

 ties may in the case of one designation lean in the aggre- 

 gate to one parent, those of another group may incline 

 to the other parent, and so on. This extraordinary 

 variability in parental relationship is particularly well 

 shown in the qualitative reactions with the various chemi- 

 cal reagents. These phenomena of variability are also 

 strikingly illustrated in both macroscopic and micro- 

 scopic properties of plamt structure. (See Part II, 

 Chapter IX.) 



9. Assistants in the Eeseaech. 

 In the studies of the starches, the histologic data 

 and the polariscopic, iodine, gentian violet, safranin, and 

 temperature of gelatinization experiments were recorded 

 by Dr. Elizabeth E. Clark, B.A. (Bryn Mawr), M.D. 

 (Women's Medical College of Philadelphia) ; and the 

 quantitative and qualitative reactions with the various 

 chemical reagents were studied by Miss Martha Bunting, 

 B.L. (Swarthmore),Ph.D. (Bryn Mawr). Both of these 

 assistants had had two years previous experience in the 

 study of starches. The macroscopic and microscopic 

 data of plants are due to Miss Margaret Henderson, B.S., 

 M.A. (University of Pennsylvania), who prepared all the 

 microscopic slides and made all of the measurements. 



