A STUDY OF WHEAT. 25 



Starch is the most generally diffused, excepting protoplasm, 

 of all vegetable substance within the cell-wall. When found 

 in the older structures, roots, stems, seeds, etc., it is found 

 nearly pure; when found in freshly growing tissue it is in union 

 with chlorophyll. Starch grains contain carbon, oxygen, hydro- 

 gen, and some mineral matter. They are insoluble in water, 

 alcohol, ether and oil, are destroyed by potassa, and colored 

 blue or violet by iodine, the color depending on the density 

 of the granule and the strength of the iodine. The starch 

 grains of different families and different species of the same 

 family differ so much in size and general appearance as to be 

 easily identified. The largest starch grains known are those 

 of the tous-les-mois which are frequently 1-12 of a millimeter 

 (1-300 of an inch) in diameter, while the smallest of the com- 

 mercial starches are those of rice, which are occasionally 1-280 

 of a millimeter (1-7000 of an inch) in diameter. There are 

 two leading theories regarding their growth. Some claim that 

 the surface of the grain is first formed, and that it grows by 

 layers, being deposited on the inside of the case, which gra- 

 dually expands until it reaches its normal size. The other and 

 more generally accepted opinion is, that the nucleus is first 

 formed, and the grain grows by means of deposits of starchy 

 matter around this nucleus, and each successive layer contains 

 less moisture than the preceding layer; this explains the appear- 

 ance of rings or laminae seen occasionally in the wheat starch, 

 but showing so plainly in the potato starch and many others. 

 In specimens which have been subjected to even a slight degree 

 of dry heat, there appears a black line or star-shaped mark 

 over the nucleus. The heat evaporates the moisture from the 

 grain, and there must be a shrinkage on the surface to corres- 

 pond with the evaporation. This is the greatest over the 

 nucleus where is the greatest moisture. In very many starches 

 there is a distinct dark cross seen when viewed with po- 

 larized light, the arms of the cross radiating from the nucleus. 

 Some botanists claim that a cross can be seen in wheat starch, 

 but if this be true, it is different for the starch of the different 

 varieties of wheat. In some grains of wheat starch there is no 

 appearance of a cross, while in some others there is a faint 

 shadow crossing the grain while polarized light is being used. 



