THE VOLATILE PART OF PLANTS. 49 



Arrow-root is starch obtained by grating and \vashing 

 the root-sprouts of Maranta Indica, and M. arundinacea, 

 plants native to the East and West Indies. 



EXP. 25, Reduce a clean potato to pulp by means of a tin grater. Tie 

 up the pulp in a piece of not too fine muslin, and squeeze it repeatedly 

 in a quart or more of water. The starch grains thus pass the meshes of 

 the cloth, while the cellulose is retained. Let the liquid stand until 

 the starch settles, pour off the water, and dry the residue. 



Starch, as usually seen, is either a white powder which 

 consists of minute, rounded grains, and hence has a 

 slightly harsh feel, or occurs in 5 or 6-sided columnar 

 masses which readily crush to a powder. Columnar 

 starch acquires that shape by rapid drying of the wet 

 substance. When observed under a powerful magnifier, 

 the starch-grains often present characteristic forms and 

 dimensions. 



In potato-starch they are egg or kidney-shaped, and 

 are distinctly marked with curved lines or ridges, which 



Fig. 13. 



surround a point or eye ; a, Fig. 12. Wheat-starch con- 

 sists of grains shaped like a thick burning-glass, or spec- 

 tacle-lens, having a cavity in the centre, b. Oat-starch 

 is made up of compound grains, which are easily crushed 

 into smaller granules, c. In maize and rice the grains 

 are usually so densely packed in the cells as to present an 

 angular (six-sided) outline, as in d. The starch of the 

 bean and pea has the appearance of e. The minute 

 4 



