24 DIFFERENTIATION AND SPECIFICITy OF STARCHES. 



of the entire mass. The quantity of ceUulose was found to be in direct proportion to the 

 resistance of the grains to swelling and solvent media. For this reason, he concludes, the 

 dense layers contain relatively more cellulose than the soft layers, and the external more 

 than the internal parts. The cellulose, he states, is not insoluble, but difficultly soluble. 

 Besides granulose and cellulose the grains were found to contain water, both in the fresh 

 and air-dried condition, and also "condensed gases;" but usually no other substances 

 were present in perceptible quantities, although sugar, dextrin, and soluble starch may 

 exist in small amount. He thought that large quantities of gases are condensed in the 

 grains, which idea was doubtless suggested by the evolution of gas during decomposition 

 processes. Differences in the reactions of starch granulose and cellulose with iodine were 

 recorded : The granulose was found to take up iodine from a weak solution and to become 

 blue before the ceUulose becomes colored, and this occurred even though the iodine solu- 

 tion had to penetrate the cellulose to reach the amylose. Wliile the amylose was colored 

 a bright red to a blue or a black, according to the quantity of starch present, pure cellulose 

 was colored a dull-red, or a brownish-red, which differences formed a means of distinguish- 

 ing one from the other. 



Studies of the mechanism of development of starch-grains led Nageli to the view of 

 growth by intussusception, and hence to oppose the theory of growth by external accre- 

 tion that was held by many of his predecessors. It must be remembered, he writes, that 

 all grains in every stage of development are solid, and that only in abnormal cases, owing 

 to solution, are they hollow. If growth takes place by deposition on the outside, then the 

 young grain and the imier layers of the large growing grain must be identical in form, 

 structure, and substance. While the forms of the two are very similar they nevertheless 

 differ very markedly, there being present in the interior of large growing grains "layer 

 complexes" which are never found in the small mature grains. In all lands of starch, 

 without exception, the substances of the young and of the large growing grains are differ- 

 ent. In the large grains there are present, from the periphery to the center, alternate 

 dense and less dense layers. During no stage of the development is there a soft layer on 

 the outer surface, but always in the growing grain a dense peripheral layer. Swelling 

 solvent media, such as hot water, acids, and alkalis, act on the inner substance of large 

 grains, as well as on the "part-grains" of "half-compound grains" (see page 66), and 

 dissolve this substance, wliile the small mature grains are not acted upon. The external 

 layer in all stages of development of the grain is the same, so that solvents disorganize 

 and dissolve the entire inner substance in both large and small grains in a similar manner, 

 but leave the outer layer in the form of a membrane. Young grains up to a certain stage 

 are entirely homogeneous, but after a time layers become evident in the interior of the 

 grains. In other grains, which in earlier stages show no structural cUfferentiation, inclosed 

 part-grains appear whereby such grains become half-compound grains. 



The phenomena of form and structure of compound grains, Nageli holds, are also 

 in opposition to the apposition theory of growth. The part-grains increase in size by 

 growth along the inner and not the outer radius. If growth occurred from outside there 

 must be pressure exerted on the outside of the grains, but the compound grams show no 

 trace of such external pressure, since the part-grains have sharp edges and corners and 

 flat surfaces. Not only, he states, is growth not by apposition, but the half-compound 

 and many of the compound grains do not originate by the fusion of simple grains, but 

 both are produced by internal processes, the originally homogeneous substance becoming 

 lamellated and divided into part-grains. He regai'ds it unlikely that there may also be 

 a deposition on the exterior of the grain, because the peripheral layer of large and small 

 and young and old grains is identical in its resistance to the action of solvents, and because 

 one would have to assume that the external layer, as it is covered by the newly deposited 

 substance, changes its nature, and that as the layers are deposited each in turn takes on 



