168 THE PLANT CELL. 



found in the cytoplasm, each of these containing an orange-red 

 pigment. The basis of each chromoplast is protoplasmic in nature. 



In the carrot, the cells of the cortex possess reddish 

 crystalloid bodies of a proteid nature, which contain carotin. 

 This pigment has some chlorophyll in its composition. Such 

 pigments are usually formed in the presence of light, oxygen and 

 Fe-salts, much as chlorophyll is in the chloroplasts (see infra). 

 It is probable that the chemical composition of many of thcin is 

 not far removed from that of chlorophyll, particularly in the case of 

 yellow or greenish-yellow pigments, some of which bear a definite 

 relationship to phylloxanthin. In many instances the colouring 

 substances exist in a cell dissolved in the ceU-sap, as in the 

 Beet-root and pericarp of many fruits. The red pigments 

 belonging to this group are changed to green or blue on the 

 addition of an alkali, and when acid is added to such an 

 alkaline solution, the red colour returns when neutralisation is 

 complete (cf. action of acids and alkalies upon litmus, a 

 vegetable pigment). The blue colouring matter in many cells is 

 known as anthomjania. 



The whiteness of many petals is due to the presence in the 

 cells of chromoplasts (leucoplasts), which reflect the rays of 

 white light falling upon them almost entirely. Intercellular 

 spaces and the convexity of the outer walls of the epidermal 

 cells may also contribute towards this result. 



The function of many of these pigments is often, as in the 

 case of the petals of flowers, of the nature of an adjuvant to 

 fertilisation, insects being attracted by brilliantly-coloured petals; 

 but where a greenish-yellow pigment is present in definite 

 chromoplasts, the assimilation of carbon-dioxide may at times 

 occur. The majority of the pigments existing in chromoplasts 

 may be extracted from them by alcohol; where the colouring 

 matter is in solution in the cell-sap, as in the Beet-root, 

 boiling kills the cytoplasm, and upsets the osmotic balance 

 of the sap in the cells, leading to an outward diffusion of the 

 pigment. The colouring matter of such permanent elements 

 as those of wood and sclerenchyma exists in the cell-walls, and 

 is the product of the decomposition of .substances deposited in 

 the walls at various times. Such pigments have, of course, no 

 vital significance once they have been deposited. 



(c) The Conditions Govei'ning the Formation of Chlorophyll 



