340 PHYSIOLOGY OF NUTRITION. 



reaction of the cell-sap is acid. If a hair is treated on a slide 

 with very dilute potash solution, the colour of the pigment is in 

 fact changed to blue ; on the addition of acid the red colour again 

 appears. In the cell-sap of the cells of Myosotis petals a blue 

 pigment is dissolved. The reaction of the sap is in this case 

 faintly alkaline. Addition of acid causes a change to red. 



If we examine under the microscope the hairs of the filaments 

 of Tradescantia stamens, we can readily make out that a violet 

 pigment is dissolved in the cell-sap of their cells. With the 

 forceps we tear a strip of epidermis from the petal of a Vinca 

 and of a red rose. In both cases the cells are seen under the 

 microscope to contain dissolved pigments. In one case, however,, 

 the pigment is blue, in the other rose-coloured. The blue, violet, 

 or red pigments dissolved in the cell-sap are classed as anthocyan. 



Many pigments occur in the cells not in solution, but associated 

 with a matrix. The colour corpuscles (chromatophores) impreg- 

 nated with pigment are for the most part of characteristic form, 

 and we first select for examination not too ripe but still well- 

 coloured hips. We prepare sections from the flesh of the hypan- 

 thium. The cells contain, besides protoplasm and nucleus,, 

 pointed orange-coloured spindles or similarly coloured triangular 

 bodies which are the chromatophores. The orange-red colour of 

 the roots of carrot plants (Daucus carota) is due to the presence 

 in the cells of chromatophores, which are easily made out under 

 the microscope as rectangular plates or elongated prisms. We 

 further prepare tangential sections from the tipper side of the 

 sepals of a just opened flower of Tropceolum majus. In the cells, 

 especially the epidermal cells, are revealed, on microscopic ex- 

 amination, many angular chromatophores, yellow in colour (see 

 Fig. 115). The brown streaks on the upper side of the sepals of 

 Tropseolum are due to the fact that the corresponding cells of the 

 epidermis contain a carmine-coloured cell-sap, as is readily proved 

 by study of suitable sections. The yellow pigments of plants are 

 almost without exception associated with a protoplasmic matrix. 

 Only rarely do we meet with them dissolved in the cell-sap. 

 This is the case, however, in the epidermal cells of the petals of 

 Verbascum nigrum. 1 The pigment of most yellow flowers is not 

 soluble in water, but dissolves in alcohol. By means of this 

 solvent, e.g., it can readily be extracted from the petals of a 

 yellow-flowered Ranunculus. The pigments of most red flowers 

 on the other hand are soluble in water, and if the petals, e.g., of 



