50 DIFFERENTIATION AND SPECIFICITY OF STARCHES. 



stroma layer is decidedly denser in grains that are undergoing solution than in grains in 

 process of growth, and here and there was noticed a pecuUar thickening of the layers in 

 the furrows which results from the flow of the stroma layer to the furrows. 



In further studies of form and lamellation, Meyer confirms the observation of Schimper 

 tliat the unequal growth of the starch-grain on different sides of the hilum is owing to the 

 unequal deposition due to the relations of the grain with the starch-builder. Meyer points 

 out that the starch-grains of Iris germanica grow most rapidly upon the side in closest con- 

 tact with the mass of the leucoplasts, and also that the closed layers are widest on the side 

 lying in closest proximity to the leucoplasts. The form of the last starch-layer deposited 

 is approximately similar to the form of the chromatophore if the chromatophore does not 

 undergo a change of form during the deposition. 



The final thickness of the layers, Meyer states, is dependent upon two factors: first, 

 the thickness of the first layers of the grain, and second, the solution in situ which removes 

 some of the starch before the occurrence of the following period of starch-growth. Like 

 many spherocrystals of other carbohydrates, starch-grains are composed of alternate loose 

 and rather compact layers, but entirely apart from this difference the layers can be differ- 

 entiated from each other by the varying proportions of a-amylose, /3-amylose, and amylo- 

 dextrin. In spherocrystals forming from a single substance in a homogeneous mother sub- 

 stance the deposition of the layers occurs in such a manner that the saturation relations or 

 other relations of the mother substance change periodically, so that a complete cessation of 

 growth, or a partial solution, does not necessarily take place. If partial solution occurs, the 

 lamellations become very prominent. Similarly, in the formation of starch-grains there are 

 fluctuations in the state of the mother substance which affect the formation of the lamella;. 



In Meyer's experiments with Pellionia, twigs were starved so that the starch-grains 

 were dissolved to such a degree as to leave only open lameUse. The twigs were now nourished 

 until the deposition of starch began, when it was found that for every day of growth there 

 was formed a thick, dense layer, and for every night a thin, soft layer. Dm-ing the day 

 the twigs were assimilating actively and the growth of the layer proceeded steacUly, but 

 at night there is a small supply of material, so that there may be deposited a thin, loosely 

 compact layer, or there may occur a partial solution of the outer layer. 



Experiments were also made by Meyer with the starch of Adoxa moschatellina and 

 Hyacinthus. The results in general showed that a relatively dense layer is deposited on 

 the grain when the clu'omatophore produces starch-substance actively and steadily, and 

 that when there is a slow and irregular production of starch-substance a thin, incompact 

 layer is formed. The thickness of the layer is always proportional to the length of the 

 period during wliich starch is continually produced. An examination of the periphery 

 of a grain that had been exposed in the chromatophore for a long time to the action of 

 diastase showed, Meyer states, that this part of the grain is never surrounded by a 

 loose laj^er, as some have supposed. The diastase penetrates every part of the grain and 

 brings about internal solution, but forms no sharply separated incompact peripheral layer. 

 Even if the internal solution plays no part in the formation of lamellae it brings about a 

 porous structure of the layers of the grain exposed to prolonged solvent action. This is 

 demonstrated, he states, by the fact that potato starch-grains, which lie for some time in 

 the sprouting tubers, are less refractive than the grains of the tubers which have sprouted. 

 This factor is, he states, hardly sufficient to account for the presence of loose, porous 

 layers in the central parts of many grains. Such a phenomenon is, he admits, explained 

 by the fact that many starch-grains in their earlier stages of growth ai'e subjected to 

 conchtions which cause the formation of open, porous layers. In Adoxa moschatellina 

 the lamellation was studied by following the stages of development. In the growing grains 

 of young shoots eccentric layers are deposited corresponding to the form of the chromato- 

 phore. As long as the layers are not affected by solvent action, all of the layers, both 



