304 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



primaiy lamellse; grains with regular outline are usually more resistant than those with irreg- 

 ular outline, in the latter the reaction beginning at the protuberances or angles; the proximal 

 end of the grains of most starches is more resistant, irrespective of the reagent, than the 

 distal end, but in other starches the reverse ; and in some grains more or less marked differ- 

 ences are observed in the behavior of different lamellge or parts of lamellse, one of two or 

 more lamellse, or some parts of lamellse, being resistive for a relatively long time after 

 the brealdng down of other parts. Generally these lamellse are centrally located, or they 

 may be noted as regularly arranged concentric bands or groups with intermediate areas 

 of gelatinized starch; and sometimes there will be a few resistant granules which may not 

 be gelatinized after a relatively exceedingly prolonged action. In this connection must 

 be considered the literature quoted in Chapter III, which indicates the existence of different 

 kinds of starch in the starch-grains, and also of the formation of reversion products. 

 The latter may ha^'e important significance in connection with the causes of the marked 

 differences in different grains and parts of grains of a given starch. 



It has long been recognized that the different lamellse of the mature starch-grain are 

 of less and less density from without inward. These peculiar variations are, it seems clear, 

 not owing to an increase in the density of each additional lamella as it is deposited, but 

 to a gradual transition of the molecular states of the inner or older lamellse to a less dense 

 condition. Such a change is explicable in the light of the ready transmutabiUty of one 

 stereoisomeric form into another owing to slight differences in attendant conditions, as 

 has been pointed out in Chapter I, page 9. The mere separation of the previously deposited 

 starch from direct contact with the plastid by the later deposited starch, age, and such other 

 incidental conditions are of themselves doubtless sufficient to satisfactorily account for 

 this transmutation. Likewise stereochemic differences in other parts, such as in primary 

 and secondary lamellse, protuberances, etc., in relation to other parts of the grains may be 

 explained in the same way. 



Differences in the forms and in the reactions of starch-grains obtained from different 

 parts of a given plant, or parts of a given organ, have been recorded by a number of obser- 

 vers, and referred to in previous chapters. In the present investigation such differences have 

 been shown incidentally in several instances, as in the case of the starches of the pith and 

 cortex of the stalk of Dieffenbachia, and in the stalk and green fruit of Musa. More- 

 over, much data of this character have been obtained that are not included in the present 

 memoir, but which will be published at some subsequent date. The differences in the 

 reactions in these cases, while as a rule not marked, are strongly suggestive of differences 

 in the starch-substances formed in the several starch-producing parts. That important and 

 characteristic differences will be found by studies of the starches from different parts of the 

 same plant, and from different parts of a given starch-forming organ, seems to be conclusive. 

 That histological differences of this kind exist will be seen by consulting especially the data 

 included in Chapter V, and it may be put down as an axiom that where different histological 

 types exist stereochemical differences exist. In some instances secondary lameUation is of 

 so peculiar a character as to be almost if not absolutely specific to the plant or plant-part; 

 as, for instance, in the striking pecuUarities exliibited by the starches of Dieffenbachia (plates 

 17, 18, and 19), Gesneria (plate 100), Phams (plate 102). 



Owing to the fact that starch is not a uniform substance, and as it appears in different 

 plants and in different parts of the same plant in the form of a heterogeneous mixture which 

 is likely somewhat variable in accordance with changes in internal and external conditions, 

 it follows as a corollary that the characteristics of a given form of starch is the sum of 

 the peculiarities of the individual components. Hence it will be found that while in every 

 form of starch the different grains or even parts of the individual grains will show more 

 or less marked differences in their forms and reactions, the sum of these peculiarities will be as 

 characteristic of the form of starch as are similar sums characteristic of a species, genus, etc. 



