VALUES OF METHODS IN THE DIFFERENTIATION OF STARCHES. 305 



METHODS EMPLOYED AND THEIR VALUES IN THE DIFFERENTIATION OF STARCHES. 



Inasmuch as this investigation was undertaken to determine primarily the molecular 

 and not the microscopical peculiarities of different starches ; and since for reasons already 

 set forth differences in histological peculiarities may of themselves be physical or physico- 

 mechanical rather than molecular, although one may be most intimately associated with 

 the other; and since differences in the Aarious forms of starch can be brought out with 

 certainty only by means that determine differences in intramolecular or intermolecular 

 arrangement, such as the physical, physico-chemical, and chemical methods used in this 

 investigation, the direction of the research has been concentrated along the latter lines. 



THE HISTOLOGICAL METHOD. 



That the histological method has a certain very marked value is evident in the fact 

 shown particularly by the investigations of the elder Nageli of the definite relationships 

 that frequently exist between the microscopical characters of the grains and species, genus, 

 and family (p. 60). But often starches may be much alike, or even seemingly identical, 

 yet be derived from unrelated species, genera, or families ; and on the other hand the starches 

 of different genera of the same family may be so entirely different as to suggest an absolute 

 absence of generic relationships. Hence if one were to rely only on histological peculiarities 

 he might be led far astray. Thus, for instance, the starches of the members of Iridacew 

 often show such striking dissimilarities as to imply an absolute absence of generic relation- 

 ship. On the other hand, the starches of Arum, Dracuncuhis, Richardia, Colchicmn, Glad- 

 iolus, Freesin, Babiann, Trianospcrrna, and Cycas show such similarities as to suggest very 

 close relationship, notwithstanding that they belong not only to entirely diSereni fa7nilies but 

 also even to chfferent orders and classes. The families here represented are Aroidew, Colchi- 

 cacew, IridacecB, Cucurbitacece, and Cycadacew; the orders are Arales, Liltales, Campanuales 

 and Cycadales; the classes are Monocotyledones, Dicotyledones, and Gymnospermw. Were 

 it not for incidental conditions, as for instance, alterations in food-supply and temperature 

 and alterations in light and darkness, the presence in the cell of crystals and the contact 

 of grains with each other which mechanically modify the forms of the starch-grains, the 

 varying mechanical influences which affect the physical relations of the plastid to the 

 growing grain, and numbers of conditions which may purelj'' mechanically affect the form 

 of the starch-grain during its development, the starch-grain would be conceived to be 

 develo])e(l along intermolecular lines as definite as in the formation of spherocrystals 

 generally. In other words, as Meyer puts it, every plastid has a "biology of its own," 

 which, applied to the foregoing, means that did not mere incidental conditions, through 

 purely mechanical or artificial ways, influence the form of the starch-grain, the form of 

 the grain would be absolutely specific to the character of the mechanism that formed it; 

 that is, the form of the grain would be as specific in relation to the plastid as are the forms 

 of the teeth in relation to the osteoblasts which deposit the osseous tissue. 



That the starch-grains are developed upon definite plans of intermolecular growth 

 would seem to follow from the laws governing the growth of crystals generally, and since 

 stereoisomeric forms of other substances are l)uilt up upon specific intermolecular jjlans 

 by which one may be distinguished from another, and that the histological forms of the 

 crystals may be modified by varying conditions attending crystallization, it follows, as 

 a corollary, that different stereoisomeric forms of starch are likewise different in their 

 intermolecular aiTangements and that these peculiarities may be obscured by conditions 

 which interfere with the development of the true histological form. Any gi^'en normal 

 rectilinear crystal owes its form to the intermolecular arrangement of its constituent 

 particles, yet the same substance with the same inherent intermolecular arrangement may 

 appear in histological forms having little or absolutely no likeness to the normal crystal, 



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