MORPHOLOGY OF HIGHER PLANTS. 



163 



to show that it is in the nature of a sphero-crystalloid, resembling 

 inuHn in some respects. Starch grains have an interesting struc- 

 ture. They vary in shape from ovoid or spherical to polygonal, 

 and have a more or less distinct marking known as the " hilum," 



Fig. 96. Successive stages in the swelling and disintegration of potato-starch grains 

 on the application of certain chemicals or heat (60°— 70° C). 



" nucleus " or the point of origin of growth. The substances 

 of which the grains are composed are arranged in concentric 

 layers or lamellae which are more or less characteristic and which 

 sometimes become more distinct on the application of certain 

 reagents (Figs. 96, 97). The point of origin of growth and alter- 



