Ver/etahle Pliysiolof/y. 



397 



compared with the formation of the bulb of the hyacinth or onion, 

 of coats successively enclosing- the whole ; the granule being 

 transparent, the boundary lines of the successive layers or " shells " 

 are seen through the whole thickness. The lamellae are of very 

 unequal thickness, and in the granules of the potato they are 

 thickest at one side, or rather end, concentrically surrounding a 

 minute point visible near the smaller end, which in the fresh 

 granules is seen to be a minute cavity filled with liquid, and in 

 dried starch appears to contain only air. Here and there in 

 potato-starch are granules of medium or small size, and different 

 form, %vith two or more of these central points or foci, each with 

 a certain number of concentric layers, and then the outer layers 

 running uninterruptedly round the whole as single coats, enclos- 

 ing double or triple granules ; this condition is far more com- 

 mon in some other plants. 



The lamellae are not only different in thickness from each 

 other and in their own different parts, but the outer layers are of 

 denser consistence than the inner ; this may be shown by their 

 action upon polarized light, but it is very evident also in their 

 behaviour when solvent reagents are applied to the granules ; an- 

 other indication of it is afforded by the fact that in thoroughly 

 dried starch the inner layers shrink, and radiating cracks are 

 perceived in the interior, running out from the point-like cavity. 



The starch occurring in the cells of the mealy structure of the 

 corn-g-rains is essentially similar to that of 

 the potato, but there are great differences of 

 form of the granules, both from potato- 

 starch and among different kinds of grain. 

 The starch-cells of wheat are delicate mem- 

 branous chambers (fig. 11, e), with closely 

 adjoining flattened walls, and they contain 

 numerous granules, of very unequal sizes, 

 the larger of which exhibit the character- 

 istic form for this plant, that of a flat 

 doubly-convex lens ; the point or cavity is 

 central, varying in size, and concentric striae 

 are less easily distinguishable than in po- 

 tato-starch (fig. 13, A). The starch of 

 barley is in grains somewhat similar, but 

 larger, the outline of the form being often 

 rather squarish, and the sides more flat- 

 tened, while the edges are thicker. The 

 starch grains of rye are much like the 

 foregoing. The larger of the starch grains 



of oats appear at first sight like irregular, rounded, more or less 

 globular bodies, in which may be perceived interconnected streaks 



Fig. 13 



A. Starch-granules of wheat. 



B. Compound starch -gra- 

 nules of oats ; the right- 

 hand figures crushed down. 

 Magnified 400 diameters. 



