MICROSCOPE IN THE GARDEN. 39 



plate 3. If we now take a drop of the solution of 

 iodine, and apply it to these cells full of granular 

 contents, we shall find that the granules assume a 

 deep-bine colour. This is the proof that they are 

 starch ; and as far as we at present know, no other 

 substance but starch has the power of assuming 

 this beautiful blue colour under the influence of 

 iodine. We have thus a ready means at all times 

 of distinguishing starch. The grains of starch are 

 of various sizes and shapes. The starch of the 

 flour of wheat has a round form, and varies in size ; 

 that of the oat is characterized by the small 

 granules of starch adhering together in globular 

 shapes. When these globules are broken up, the 

 grains appear very irregular. Grains of wheat 

 starch and oat starch are seen in figures 62 and 63, 

 plate 3. In the arrow-root called " Tous lea 

 Mois," the grains of starch are the largest known, 

 and, like those of the potato, they look as if com- 

 posed of a series of plates laid one upon the other, 

 gradually becoming smaller to the top. This is 

 seen at figure 65, plate 3. These lines do not, 

 however, indicate a series of plates, but appear 

 more like a series of contractions of a hollow vesicle 

 or bag. This vesicular appearance of starch may 

 be made apparent by gently heating it, after 

 moistening, over a spirit-lamp on a glass slide, or 

 by dropping on it a drop of strong sulphuric acid. 

 This action of the starch-granule appears to be due 

 to the fact that the starch is converted into gum by 

 the action of the heat on the sulphuric acid. Sago 

 and tapioca are almost entirely composed of starch, 

 and may be easily examined under the Microscope. 

 Granules of sago are represented in figure 67, and 

 those of tapioca at figure 68 ; they are readily 

 distinguished by their size. The starch granules 

 are insoluble in water, but they are easily diffused 



