197 



i6o C. The discs are thinnest in the middle and from this centre the needles 

 radiate. The discs resemble natural wheat starch as well in shape as in size. 

 With polarised light I could not, however, perceive anything of the axial cross, 

 which is so very obvious in natural starch. I suppose that it does exist, but is 

 too feeble to be observed. It is, namely, a fact that the structure of the spherites 

 and discs is much looser than that of natural starch, so that in a volume unit 

 of the latter many more needles occur than in the discs and spherites. If now 

 the double refraction of the separate needles be not great, their united power in 

 the discs need not necessarily show the same as is seen in the natural grains. 



That de double refraction of the common starch grains reposes on their 

 crystalline nature and not on tangential and radial tensions, may be concluded 

 from the fact, that the axial cross is in the usual way perceptible in soluble starch. 

 As this substance is prepared with strong hydrochloric acid, whereby from 10 

 to 16% of the dry substance is extracted, it must be concluded that all tensions, 

 originally present in the grain, disappear. 



That the discs may also be obtained from potato starch is demonstrated in 

 Fig. 3, where 10% potato starch, after boiling and gelatinising in distilled water, 

 in a 100 cm 3 beakerglass, heated to 125 C. during 3 l /2 hour, and after 24 hours 

 of crystallisation in a room of about 16 C., is figured 600 times magnified. 



By moving the coverglass on the slide, many discs may be observed laterally, 

 as is clearly seen in the photo. In the preparation of wheat starch used for 

 Fig. 3, all the grains are lying on their broad side. 



The crystal discs of the starch are now and then referred to in literature 

 as Jacquelain discs, but without any allusion to their crystalline structure. 

 Jacquelain himself, who first mentioned these grains, called them granules 

 de fecule* 1 ). 



After having become acquainted with the described facts and found them 

 confirmed for other species of starch, I convinced myself that the natural starch 

 grain also it built up of crystal needles radiating from the dot or hilum. This 

 may best be seen in soluble potato starch, very cautiously heated in the micro- 

 scopic preparation on the slide under the coverglass, when all the stages of the 

 dissolving in hot water can be followed. The tiny radiating crystal needles then 

 become visible in a ring-shaped arrangement, such as might be expected from 

 the structure of the starch grain itself. It seems that the length of the needles 

 corresponds with the thickness of the rings. 



From the preceding I conclude, that the formation of the starch grain takes 

 place in the following way. The amyloplast produce's granulose, which in the 

 interior crystallises to small spherites, just as in a solution. But this granulose 

 production occurs periodically and so the process of crystallisation gives rise to 

 the formation of the layers of the grain. 



To explain the great difference existing between starch gelatinised at 100 C. 

 and that heated to 150 and 160 C. it must be accepted that in the starch grain, 

 beside the granulose, an incrustating substance exists, functioning as a protecting 



') J. A. Jacquelain, Memoire sur la fecule. Annales de Chimie et de Physique. 

 T. 63, pag. 173, Paris 1840. Much in this treatise is incorrect and obscure, else the discs 

 would certainly already earlier have drawn general attention. 



