280 M, Martin on the Amylum Grains of the Potatoe. 



the kernel is situated. On the surface minute fissures appear, 

 two of which almost regularly diverge towards the thicker end 

 of the grain. The grain continues to be depressed inwards until 

 a cavity is formed, which is surrounded by an elevated ridge. 

 In proportion as the grain swells up, this ridge increases in cir- 

 cumference and decreases in breadth, that is, continues to get 

 flatter, until fissures, mostly of a stellated form, appear in the 

 hitherto little altered thicker part of the grain. The process is 

 now very rapidly developed, and it is very difficult for the eye to 

 follow it. Suddenly something is torn off, the grain is extended 

 lengthways, and in the next moment a wrinkled skin of a round, 

 generally oval shape lies on the glass. Middle-sized and small 

 grains exhibit this shape most distinctly ; and they have usually 

 only one longitudinal wrinkle, the upper and lower ends of which 

 are pointed. The constant appearance of this wrinkle is import- 

 ant for the development of my theory. 



4. When, as mentioned above, very few grains are employed, 

 so that after boiling they remain properly separated by interve- 

 ning spaces, if the temperature has been the proper one, the 

 smaller grains appear as round disc-like skins, almost without 

 wrinkles. The middle and large-sized ones are also apparently 

 transformed into flat discs. If the glasses are removed from the 

 stage, pressed against each other, and at the same time slightly 

 moved from one side to the other, again placed on the stage and 

 viewed by an obliquely-directed light, it will be seen, in propor- 

 tion to the success of the experiment, that the wrinkles of the 

 skin are either entirely smoothed or merely pressed down. In 

 the former case the discs so produced have a perfectly round or 

 oval form. In the latter case the contour of the discs remains 

 slightly contracted or twisted, which is chiefly the case with very 

 large grains. In the course of my investigations I discovered a 

 method of delaying the entire process of boiling, by which the 

 above-mentioned discs are obtained in a perfectly secure manner. 

 This may, perhaps, make the experiment less striking, but it 

 answers admirably for the verification of my theory. 



By the action of tincture of iodine the amylum grains are 

 contracted, i. e. are condensed, being transformed into iodized 

 amylum. If a small drop of tincture of iodine be added to a 

 quantity of water, and the whole well mixed, amylum grains 

 placed in this iodized water turn light blue, dark blue, or almost 

 black, according to the quantity of iodine employed. The pre- 

 cise quantity, which a few experiments will determine, is that 

 which renders the grains of a delicate sky-blue colour without 

 depriving them of their transparency, or obliterating the layers, 

 or at least the traces of them. If too little iodine be used, the 

 process goes on too rapidly ; if too much, too slowly ; the grain 



