STARCH-SUBSTANCE, AND THE STRUCTURE, ETC., OF THE STARCH-GRAIN. 49 



green" leucoplasts of potatoes, he observed colorless grana lying in the stroma, and these 

 he designatetl albigrana, but since that time he has not studied them. Inasmuch as only 

 the chromatophores which contain grana; separate oxygen, it seemed to him likely that 

 the grana constitute the ajiparatus of assimilation. The colorless as well as the green 

 parts of the chloroplasts have, he states, the capacity of forming starcli-substance. 



The starch-grain, Meyer holds, grows entirely within the chloroplast, and the approxi- 

 mate proportion between the thickness of the chromatophore layer and the starch-layers 

 growing below it makes it probable that the chromatophore controls the production of 

 starch-substance. The stroma probably produces the starch, because the grain is most 

 actively added to where the layer of stroma is thickest. Chromatophores embedded in a 

 relatively fine-grained emulsion of cytoplasm show the simplest form a rather viscous 

 drop. But the form varies and is alterable in relation to contents which originate in the 

 chromatophore. The various forms of these bodies have a close relationship to the forms 

 of the starch-grains growing in them, provided that the shape of the chromatophore is 

 retained for a sufficient length of time. 



Protein crystals growang in the chromatophore produce a change in form which may 

 be constant for a long time, and they are very important in relation to the growth of the 

 starch-grain. Pigment crystals act in a similar manner, and occasionally influence the 

 form of the starch-grains. But the most far-reaching changes in the forms of the chroma- 

 tophore are due to the starch-grains themselves. Not only does the growing starch-grain 

 act upon the shape of the chromatophore, but the varying form of the chromatophore 

 reacts upon the growing grain. There are cases where there are simultaneous growths of 

 eccentric starch-grains and chromatophores, when after a certain stage in development 

 both grain and chromatophore increase in size yet constantly retain the same form. The 

 young chloroplasts of Dieffenbachia are mostly spherical and contain mostly centric starch- 

 grains, a few eccentric. On further growth all of these grains were found to become elon- 

 gated and eccentrically layered, so that the chloroplast bulges out on one side into a thin 

 membrane. A grain wliich is centric at first may develop into an eccentric or concentric 

 grain, according to the nature of the cliromatophore, which is influenced by the surrounding 

 cytoplasm. The pressure of a relatively thin but viscid layer of cytoplasm upon the cliro- 

 matophore exerts a marked influence upon the shape of the chromatophores, and also 

 therefore upon the starch-grains growing within them. The pressure of the cytoplasm, 

 together with the viscosity of the cliloroplast and the pressure of the growing starch-grain, 

 gives rise to an accumulation of chloroplast substance at two diametrically opposite points 

 of the starch-grain, so that the chloroplast assumes the form of a thin-walled sac with thick- 

 walled ends. Several grains may grow in one chromatophore. 



Pellionia serves as a good example, Meyer states, of the change of form of such clilo- 

 roplasts as contain two starch-grains. In well-nourished types of this plant the growth 

 of the starch-grains normally exceeds that of the chloroplasts. The margins of the grains 

 push diagonally through the chloroplast, and as the grains grow the tendency is to push 

 the chloroplast out into a layer over the contact surfaces of two grains. In Dieffenbachia 

 the chloroplasts are of rather thick consistency, so that two growing starch-grains press 

 out the layer of the chloroplast substance between them more slowly, and owing to the 

 greater mutual pressure of the grains the grains assume an irregular shape. A change in 

 the form of the chromatophore that is far-reaching and very significant in its influence 

 on the ultimate form of the starch-grain is brought about by an active solution of the 

 contained starch-grains. Meyer states that if one observes in Dieffenbachia the chloro- 

 plasts which surround the normal starch-grains during the various stages of solution, it 

 is seen that the main mass of the chromatophore becomes rounded and that the thin layer 

 of the chromatoplast which covers the largest part of the grain is closely joined to all of 

 the transverse furrows that originate in the grain. At times he observed that the thin 



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