282 M. Martin on the Amylum Grains of the Potatoe. 



cluced. During the progress of the rolling up, the space a is of 

 course constantly decreasing, while the parts on the inner edge 

 of the band offer a resistance. This resistance must be overcome 

 by contraction, in a direction tangental to the internal circum- 

 ference ; consequently a part of the band which has been by 

 accident, or from the unequal thickness of the vesicle, rolled up 

 before, or more than the rest, prevents the remaining part from 

 rolling itself up. Hence the cause of the elliptical form of the 

 band. The space at a now becomes continually smaller, until 

 the interior edges approach so close that they are joined together, 

 and the small hole hitherto remaining is closed. The amylum. 

 grain with its elliptical layers so far complete is represented by 

 fig. 3. 



Y\ r e have obtained, as it were, a sketch of the geometrical con- 

 struction of the amylum grains, according to which the kernel is 

 not a primary substance, but a secondary form only. Whether 

 this space is occupied by a liquid or by air has nothing to. do 

 with the theory of formation here developed, and is a subject for 

 special investigation. How far this theory agrees with micro- 

 scopical observation must be shown by experiment. As for the 

 physiological questions arising from this theory, they must be 

 reserved for more expert pens than mine. 



7. Let us now proceed to compare the theory hitherto admitted 

 with the new one as explained above. When the vesicles, coloured 

 with tincture of iodine and pressed flat, are once seen to revolve 

 round their axes, it seems decisive that no such thing as splitting 

 through and through takes place; for this skin is so homo- 

 geneous and so transparent, that even the slightest fold is easily 

 perceived. Schleiden, although he calls the product of the last 

 stage of boiling a thick skin, and not a vesicle, seems already to 

 call in question the complete splitting open, for he expressly 

 says, that during the boiling the split is transformed into a large 

 cavity. Now, I ask, what has become of the layers, which must 

 assuredly possess much more substance than the external skin 

 of the unboiled grain ? Are they dissolved, or merely separated, 

 and one fixed in the other ? Has the smallest one surrounding 

 the kernel, and the larger one close to it, and the third still larger 

 one, and, in fact, have all the layers become increased, or dimi- 

 nished to the exact size of the external skin in order to form with 

 it a large bag ? or are the interior soft layers (so called) boiled 

 away to a jelly-like mass, which remains invisible within the bag 

 and is pressed flat with it ? RaspaiPs assertion, that part of the 

 amylum grains is dissolved, belongs, as is well known, to the 

 things long since refuted and forgotten. That the skins should 

 lie fixed one within the other and yet not differ in their dimen- 

 sions, nor any fissures appear, nor the disc be thicker in the 



