28 II. FOOD RESERVES IN SITU. 



wall of the cells (m) is pretty thick. In the adjoining figure the 

 three middle cells are completely, the surrounding ones only 

 partially, represented. In each cell can be seen the large starch 

 grains (am), and with some care also the small grains (al) which 

 lie between them. These small grains are, on their part, embedded 

 in a very finely granular ground substance (p). From thin 

 parts of the section many starch grains will have fallen out ; a 

 hollow of similar form and size in the granular mass will indicate 

 these places. The small grains are aleurone or protein grains ; 

 they lie in the ground substance of the cell. If we run iodine 

 solution, best in the form of glycerine iodine, into the preparation, 

 the coloration which ensues gives us immediate information as 

 to the individual constituents of the cells. The drop of iodine 

 solution is placed at the edge of the cover-glass ; as, however, 

 the iodine solution diffuses very slowly in the glycerine, and it is 

 not our present purpose to study the progress of the reaction, we 

 accelerate it a little by slightly raising the edge of the cover-glass 

 with a needle, and so facilitate the mixture of the iodine with the 

 glycerine. A second needle placed at the same time against the 

 opposite edge of the cover-glass prevents it from slipping. The 

 starch grains colour blue to violet ; the aleurone grains and the 

 ground substance yellow. If sections of pea are laid in a drop of 

 alcoholic borax-carmine solution, in a very short time the ground 

 substance, and also almost simultaneously the aleurone grains, 

 are stained dark red ; the starch grains remain colourless. The 

 reaction becomes especially striking if, after the section is 

 thoroughly soaked in the carmine solution, this is replaced by 

 dilute glycerine or by water. This is done by sucking out the 

 carmine solution by a piece of blotting-paper placed at one edge 

 of the cover-glass, while at the same time the water or dilute 

 glycerine is run in under the opposite edge. If a section is 

 placed in Millon's reagent, the starch grains swell very strongly, 

 and become unrecognisable ; aleurone and ground substance are 

 immediately disorganised ; the disorganised mass, however, after 

 some time, takes on a characteristic brick-red colour. If still 

 another section is laid in watery iodine green or methyl green, 

 after a short time there appears in each cell, between the other 

 constituents, a greenish-blue spot of rather indefinite outline. 

 This spot is the Nucleus (n). The other constituents of the cell 

 have not stained ; the starch grains are just a little swollen (they 

 show radial clefts, which are wanting in glycerine), and the aleu- 



