122 



PHYSIOLOGY OF NUTRITION. 



fatty ground substance in which the aleuroiie grains lie, rapidly 

 assumes a dark colour. In the aleurone grains of Ricinus we 

 can similarly prove the existence of proteid crystalloids by ex- 

 amining delicate sections of the endosperm in Osmic acid (see 

 Fig. 40). 



We prepare delicate transverse sections from the cotyledon of a 



ripe pea. On the cut 

 surface we place a 

 drop of glycerine, and 

 examine the section in 

 glycerine, diluted with 

 about one-third its 

 volume of distilled 

 water. The micro- 

 scopic structure which 

 we observe is depicted 

 in Fig. 41. We see 

 roundish cells with tri- 

 angular intercellular 

 spaces between them. 

 In the cells we find a 



FIG. 42. Transverse section of a wheat grain (Triti- ,, , 



cum vulgare). p, fruit coat ; t, seed coat. In the ad- Ver 7 nnely granular 



jacent endosperm cells, al, aleurone grains ; am, starch matrix. In this are 

 grains; n, cell nucleus. Magn. 210. CAfter Strasburger.) 



embedded the fairly 



large starch grains and the small aleurone grains. On the addi- 

 tion of Iodine, the starch grains stain blue ; but the ground sub- 

 stance, and also the aleurone grains, which consist essentially of 

 proteid material, stain yellow. Delicate sections through the 

 cotyledons of a pea, stained with methyl green Acetic acid, sho\v 

 that in each cell there is present a nucleus, which has become 

 greenish blue in colour. If we prepare a delicate transverse section 

 of a ripe wheat grain, moistening the cut surface with glycerine, 

 and lay it in glycerine for examination, we shall find that immedi- 

 ately below the fruit coat and seed coat, which we shall discuss 

 more particularly in another place, there is a layer of rectangular 

 cells. No starch grains are present in the cells, but they contain 

 many small aleurone grains. The cells of the more deeply lying 

 tissue contain large quantities of starch (see Fig. 42). 



1 See Kienitz-Gerloff, Botan. Zeitung, 1891, where the literature is given. 

 See also Strasburger's Practical Botany. 



