198 



Meantime the grains warp and twist and writhe about. Separated 

 before by considerable spaces, they now block up the whole field, 

 and their outlines gradually disappear until the whole is a homo- 



The action of sulphuric acid differs a little. There is the same 

 uneasiness of the grains on the approach of the acid. Meantime 

 the concentric lines grow very sharp and distinct. When struck 

 by the acid, the grains swell until nearly globular, then a fissure 

 appears, generally in the vicinity of the nucleus. The grain is rent 

 from side to side, and a mass of liquid matter with some grains 

 intermixed, shoots out with so much force that it is sometimes 

 carried to a distance of two or three times the diameter of the 



From these observations it appears evident: that the outer 

 layers are more dense than the inner ; that the semi-liquid interior 

 absorbs water or other fluids by endosmose until the exterior is so 

 much expanded as generally to burst ; that the outer layers are 

 much less readily dissolved than the inner. 



The use of the polarizing apparatus shows in a striking and 

 beautiful manner that the nucleus coincides with the optical centre 

 of the grain— which might be translated that the layers are really 

 regularly arranged around the nucleus. It also brings out more 

 clearly the rings themselves. If abundance of light is used, and 

 a plate of selenite is inserted between the object and the analyzer, 

 a cross of colors of rare beauty is seen on the grains. If the 

 polarizer is now rotated, the play of colors is very beautiful. 

 The interesting fact to us, however, is that the arms of the color- 

 cross meet at the nucleus. 



We have thus seen that the starch grain is an organized body, 

 composed of layers arranged about an eccentric focus, and that 

 these layers increase in density from within out, the innermost 

 being comparatively soft. 



