CHAPTER IV. 



THE DIFFERENTIATION OF THE STARCHES FROM DIFFERENT GENERA, 



SPECIES, ETC. 



The differences in the histological characteristics of starches from different kinds of 

 plants attracted the attention of some of the earliest workers, and as far back as 1834 

 Fritzsche (page 64) noted that not only were the forms very various, but often were so 

 characteristic as to indicate the genus or family, or even the species. This observation 

 received more or less confirmation in the investigations of Schleiden and others. In fact, 

 the differences in the forms of the grains of certain of the familiar articles of commerce, 

 such as cereals, beans, peas, potato, etc., are so marked as to have given the impression 

 to superficial observers that the microscopical appearance is typical for each individual 

 starch, whatever its source. 



That the starch of each species is specific in certain of its characters is obvious from 

 the results of the present investigation, but it would be hazardous, as shown by the records 

 of Niigeli and others (Chapter V), to rely solely, or even often, in any important measure, 

 upon the histological features of the grains. In Plates 13, 51, 68, 75, and 78, figs. 77, 301, 

 407, 441, and 465, starches are pictured from species belonging to entirely different genera. 

 If such grains were mixed it does not seem likely that the microscopist would detect that 

 it is a mixture, yet such could readily be shown b}^ other means. In other words, the 

 morphological method by itself may be entirely misleading, yet when coupled with other 

 methods may have very great value. By the histological peculiarities it might be possible 

 to state that this or that starch did not come from a certain species or genus, yet it might 

 be impossible to assign it to its proper source, because of its seeming histological identity 

 with certain other starches which may not have even the remotest relationship. 



The investigations along various independent lines of inquiry have demonstrated that 

 we have a number of means which collectively will not only enable us to differentiate the 

 starches of different genera, species, varieties, and hybrids, but also of different parts of 

 the same plant, indicating thereby a specific biologic relationship between the peculiarities 

 of the starch-grains and the specialized plastids which form them, so that even in the same 

 individual, if there are a number of groups of these starch-forming cells, each group being 

 differentiated from the others, each will produce a form of starch which logically should 

 have individual distinctive liistological characteristics; but such characteristics would not 

 of themselves necessarily imply stereochemic differences. 



Comparative investigations of starch have been pursued by various methods, such 

 as the following : 



(1) The histological method, by which are studied the form and size of the grains, posi- 



tion and character of the liilum, characteristics of the lamella?, orientation, etc. 



(2) The proximate constituents and other features as regards general chemical compo- 



sition. 



(3) Color reactions with various reagents. 



(4) Reactions with aniline dyes. 



(5) Reactions with swelling reagents. 



(6) Temperature of gelatinization. 



165 



