30 DIFFERENTIATION AND SPECIFICITY OF STARCHES, 



power of perceiving these differences depends. The outermost, most dense, and least 

 watery layer is succeeded by a more watery layer beneath, and this in turn is followed by 

 a still more watery layer, and so on until the innermost and least dense and most watery 

 layer surrounds a very watery part, the nucleus. 



Sachs believes that the hypothesis of the growth of the starch-grain by intussuscep- 

 tion alone affords an explanation of all of the phenomena arising diu^ing the growth of 

 the grain. New particles of formative material become, he tliinks, intercalated between 

 those already existing, both in radial and tangential directions, by which means the pro- 

 portion of water at the points of deposition is lessened. Did the formation of layers occur 

 by external deposition, grains would be formed in which the outermost layer is the most 

 wateiy; but this never occurs, because the outermost layer is always the least watery and 

 the most dense. According to the view of growth by apposition, he contends that the 

 nucleus would possess the properties of young grains, which are dense, whereas in mature 

 grains the nucleus is always soft. The theory of growth by apposition he believes could be 

 accepted to explain only the formation of partially compound grains if we were to assume 

 that the common layers which inclose the single simple grains had been deposited about 

 them, in wliich case the common layers would have a different form and the fissures in 

 the interior of such grains would remain unexplained. 



In 1874 a monograph appeared by W. Nageli (Beitrage zur naheren Kenntnis der 

 Starkegruppe in chemischer und physilogischer Beziehung, Leipzig, 1874, S. 106) in which 

 he treats especially of the effects of dilute acids on starch, and of the means of preparation 

 and the properties of aviylodextrin. (See Chapter III, p. 114.) He notes that while starch 

 in a natural condition is insoluble in water, it becomes soluble after long soaking, or when 

 the grains are broken; and that there are several modified forms of starch which are char- 

 acterized by their different powers of resisting solution and by their reactions with iodine. 

 In the solid state these forms are said to take color in the order of blue, violet, red, orange, 

 and yellow, as their power of resistance to solution and their affinity for iodine increase. 

 Iodine added to a starch solution will always turn it blue, because, he states, on boiling 

 with water the other modifications gradually go over into the blue-reacting form. Tliis 

 latter form, being the more readily soluble, possesses the power of absorbing the less soluble 

 modifications; the disappearance of the former precipitates the latter. The various kinds 

 of starches, he states, may be distinguished by the different proportions of these modified 

 forms. The difference in the substances composing the starch groups may, he believes, 

 be a chemical one, but that it more likely rests on the physical condition of greater or less 

 distribution. 



Musculus (Botanische Zeit., 1879, xxxvii, 345) accepts the view of C. Nageli that 

 starch consists fundamentally of two substances (granulose and cellulose), but he goes on 

 to show that the cellulose (referred to by him as amylo-cellulose) is nothing else than an 

 insoluble modification of granulose. Granulose can by drying, he states, be transformed 

 into cellulose, and cellulose can be transformed by sodium hydroxide into granulose. If 

 alcohol be added to the sodium-hydroxide solution of cellulose, a gelatinous precipitate 

 results which, after repeated wasliing, shows all of the properties of granulose. This 

 precipitate is completely soluble in hot water, and the solution is colored blue with iodine. 

 If the precipitate is dried, it vmdergoes a partial transformation into cellulose. 



The first of an important series of contributions which have had a marked influence 

 on our views, even up to the present, was published by Schimper (Botanische Zeit., 1880, 

 XXXVIII, 881; 1881, xxxix, 185, 201; 1883, xli, 121), in which he studies the structure 

 and mechanism of formation and other properties of the starch-grains, and also the specific 

 starch-forming structures of various plants. He records in the first article that if the 

 chlorophyl-grains are spherical, the starch-grains may appear at all points of the chlorophyl- 

 grains; but if the form is plate-like, the starch-building is limited to the equatorial zone, 



