402 Collins.—The Structure of the Integumentary System of the 
usually held that of the starchy cells of the endosperm, this layer at least 
remains living. 
Fresh unripe, but well-developed grains were also experimented with ; 
in all cases the phenomena observed were similar to those described for 
the dry mature grain when put into contact with iodine. 
Wheat and oats exhibited the same general phenomena. 
Fig. 8. Distribution of iodine in endosperm. Serial transverse sections from a grain steeped 
in iodine solution. The blackened areas, except those representing the chalazal tissues, indicate 
the coloration of starch by iodine. (See Key Fig. 8 a .) 
A further test was made by embedding grains in iodine-gelatine. 
A strong solution of iodine was made up with 12 per cent, gelatine, the 
iodine solution being added just before the gelatine set. The grains were 
immersed and arranged in rows in the glass dish. The diffusion of iodine 
was slower and the process of blueing was easily watched ; it proceeded 
in the way already described and figured. Another advantage lay in the 
