in THE COLOURS AND PIGMENTS OF PLANTS 69 



in the amount of acid present in the cell-sap. Other 

 plants again show an extraordinary constancy in the 

 tint of the anthocyan of the petals, the fruitlessness 

 of florists' efforts to produce blue roses is said to be 

 the result of some peculiarity of constitution of the 

 pigment which makes the tint impossible. 



The colours of the lipochromes vary from yellow 

 through orange to red, and they colour such flowers 

 as daffodils, jonquils, yellow and red lilies, such fruits 

 as those of the tomato, the melon, the honeysuckle, 

 the asparagus, the lily-of-the-valley, and so on. It 

 is interesting to note, however, that the pure red 

 lipochromes, as distinct from the orange, are rare if 

 not entirely absent in plants (see Chap. II. under 

 Lipochromes). As to origin, the chromoplasts arise 

 in -much the same way as chlorophyll corpuscles do, 

 and indeed in many cases the unripe fruit or un- 

 developed floral leaves contain ordinary chlorophyll 

 corpuscles. As development proceeds the chlorophyll 

 disappears just as in the case of autumnal leaves, 

 and the highly coloured lipochrome is left. Various 

 names have been given to the different lipochromes 

 of flowers and fruits, but there is some reason to 

 suppose that they all arise from the pigments normally 

 associated with chlorophyll. Sometimes the lipo- 

 chromes occur in ripe fruits and flowers as crystals, 

 the original envelope of protoplasm having entirely 

 disappeared. The colours of most flowers and fruits 

 are caused either by anthocyan or lipochrome pig- 

 ments, or by a combination of the two, but there are 

 a few which are coloured by a yellow pigment of 

 unknown affinities dissolved in the cell-sap. Such are 

 the colouring-matters of the orange and of the dahlia. 



