MICRO-CHEMISTRY OF THE CELL. 29 



On each side of the hilum a number of layers will be 

 seen, constituting the stratification of the grain. 



The layers near to the hilum are concentric with it, 

 and are complete ; the more external layers are excen- 

 tric, and many of those between the hilum and the 

 broad end of the grain will be seen to be incomplete ; 

 hence the layers are more numerous between the hilum 

 and the broad end than between the hilum and the 

 pointed end. 



Here and there will be seen a compound grain, 

 consisting of two small grains in contact b} r their broad 

 ends, and invested by several layers common to both. 



!>. The Micro-Chemistry of the Cell. 



I. The CELL-WALL. 



a. Cellulose cell-walls, 

 i. Coloured faintly yellow by iodine. 



ii. Coloured violet on treatment with Schulze's solu- 

 tion (p. 22). 



iii. Coloured blue on treatment with iodine and 

 sulphuric acid. 



In some cases the cell- wall turns blue when it is treated with 

 iodine alone, a substance allied to starch being probably present 

 (amyloid) ; instances of this are, the asci of Lichens, the bast 

 in the stem of Lycopodium and in the root of Ruscus, the 

 endosperm-cells of Pceonia, and the cells of the cotyledons of 

 various Leguminous seeds. 



In other cases the characteristic reactions are not given on 

 treatment with Schulze's solution, or with iodine and sulphuric 

 acid ; instances of this occur in the tissues of young seedlings, of 

 growing-points, of the cambium, and of Fungi. In the case of 

 young tissues it suffices to treat them previously with hydrochloric 

 acid or with solution of potash for a short time ; they then give 



