82 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



(8) The forms or shapes of the starch-grain are variable in plants of different species, 

 and in the same plant, and in different parts and even in the same part of a given plant, 

 antl are affected to some extent by the age of the plant and by changes in nutritive condi- 

 tions; but the starch-grains of any given plant have characteristics in conmion wliich are 

 sometimes more or less chstinctive of the family, genus, species, etc. Greater departures 

 from a given external form should be expected in spherocrystals produced under the 

 pecuUar, complex, and varying conditions of stai'ch formation than under the conditions 

 under which rectihnear crystals and spherocrystals generally are formed. In the production 

 of the starch-crystal the growth of the crystal in all organisms, except in the lowest that 

 produce starch, is, it seems, by means of specialized protoplasmic structiu-es acting in 

 conjunction with a cell-sap of peculiar, complex, and variable composition, while in the 

 formation of crystalline substances generally the growth is ordinarily from molecules in 

 a solution of simple composition and of \'irtually unchanging composition, except in so far 

 as is concerned the loss of the mother-substance from the solution, and attended by com- 

 paratively unimportant changes in external conditions. Even though there be variant 

 forms of the mature starch-grains or starch-spherocrystals in a given plant or given part 

 of a plant, the molecular constitution of the starch-substance or the mean molecular con- 

 stitution of the combination of starch-substances constituting the individual grains may be 

 precisely the same, the vicarious forms representing distortions such as occm* in the for- 

 mation of rectilinear crystals when subjected to mechanical pressm-e and other conditions 

 which give rise to malformations. It follows from this that while there may be a specific 

 stereoisomeric form or combination of forms of starch in relation to each species or each 

 genus, etc., conditions incidental to crystalUzation might so affect the form of the grain as to 

 seemingly produce a shape that is foreign to thatwhich might be regarded as belonging to the 

 type of the species or genus. It would, therefore, be as hazardous to conclude that because 

 starch-grains from any two sources differ in form they must necessarily differ in chemical 

 constitution or stereochemic form; or because they are of like shape they must necessarily 

 be of the same chemical constitution or stereochemic structure. The fallaciousness of such 

 conclusions will be clearly shown in subsequent pages. Having a gi^-en substance, variations 

 in crystalhne form must be expected when certain attendant conditions are variable. 



In the formation of starch-spherocrystals fom* cooperative factors must be conceded 

 as being continually operative: One, non-biological, which is common in the formation* 

 of spherocrystals of sugar, unUin, leucin, etc., in vitro, tends specifically to the production 

 of circumUnear crystals, which consist of radial aggregates; another, biological, which oper- 

 ates in the living organism to maintain a non-crystalline or amorphous condition; and 

 another, the presence of foreign bodies, such as crystals of proteins or oxalate, etc., or of 

 multiple starch-grains which by mechanical pressure or otherwise influence the forms of 

 the grains; and finally, various conditions, such as changes of temperature, composition 

 of the cell-sap, etc., which cause a given substance to crystallize in different forms. In 

 other words, the tendency of the starch-substance is to crystallize, which is opposed by 

 the tendency of bodies associated with protoplasmic process to remain in solution or in 

 pseudo-solution, or to be deposited in a colloidal or amorphous soUd form, as in the soft 

 and the osseous tissues. Rectilinear crystals of entirely different substances may have 

 precisely the same external features; and, on the other hand, crystals of precisely the same 

 substance may have different external features, in other words, appear in different phases 

 or forms. This doubtless applies to the different starch substances and to the stai'ch sphero- 

 crj^stals. Therefore, the peculiarities of molecular structure, as determined by various 

 reagents and by the polarizing microscope, enable us to determine the presence of different 

 stereoisomeric forms — or, in other words, to show differences in chemical constitution, 

 whereas differences in histology may be mere expressions of variations due to physical or 

 physico-mechanical conditions. 



