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mense number of bodies of two sorts. The most striking are 

 ovoid bodies of considerable apparent size, often showing a series 

 of eccentric rings, the one within the other. Sometimes the rings 

 are seen to be arranged about a dark point or nucleus. Mixed in 

 with these ovoid bodies are large numbers of much smaller disk- 

 shaped ones, without apparent rings. These two sorts of bodies 

 are the starch granules of the potato, 'it is no unusual thing to 

 find two pretty distinct sizes of starch grains in the same plant. 

 There are intermediate forms of all sizes, but the two sizes re- 

 ferred to so much predominate as to strike the attention at once. 

 The grains are packed in very elosely together in much larger cells 

 the cut edges of which can be distinguished, although they are 

 very transparent. Here and there in the section are spots without 

 starch grains and with much finer tissue. These are sections of 

 the vascular bundles where longer and fibre-like cells and vessels 

 which arise from the stem pass through the tuber. Toward the 

 edge of the potato, too, the starch grains are seen to grow less 

 numerous and the cells smaller with thicker walls. 



To render the position of starch and cell-walls still more evident, 

 let us apply a little of the aqueous solution of iodine to the speci- 

 men. This can be readily done by placing a drop at the edge of 

 the thin glass cover. It will be gradually drawn under to mingle 

 with the water. Meantime its progress and its effect can be 

 watched with the eye at the microscope. Should the iodine not 

 pass readily under the glass cover, its progress can be hastened 

 by placing a bit of blotting paper in contact with the cover on the 

 other side. As it absorbs the water, the iodine will pass in to 

 supply its place. As the iodine comes in contact with the cell- 

 walls they are stained a rich gold-color. At the same time, a 

 series of changes is taking place in the starch. The grains were 

 at first colorless and transparent; as the iodine reaches them, 

 they are stained, first yellow, then red, violet, blue, and finally an 

 opaque black blue, if the iodine is strong enough. Here we have 

 the cell-walls colored one tint, and the starch another, and.it is 

 very easy to determine their relative positions. 



The use of iodine is the most usual test for starch, and the re- 

 sulting blue color is just as certain in the blue grains under the 

 microscope as in the starch-paste in use by chemists. If sulphuric 

 acid is added to the specimen, the cell-walls gradually turn 

 blue too. 



