114 CHEMISTRY OF PLANT LIFE 



allow the two layers to separate. The carotin will now be in 

 the upper layer of petroleum ether, and the xanthophyll in the 

 lower alcohol layer; these layers may be drained off separately 

 and the solvents evaporated in order to recover the pigments in 

 dry form. 



Lycopersicin (or lycopin) is a hydrocarbon pigment having 

 the same formula as carotin. It is, however, brilliantly red in 

 color, and crystallizes in a different form and has a different 

 absorption spectrum from carotin. It is the characteristic pig- 

 ment of red tomatoes, and is found also in red peppers. Yellow 

 tomatoes have only carotin as their skin-pigment, while lyco- 

 persicin is usually present in the flesh of the ripe fruits of all vari- 

 eties and in the skin of red ones. It has been shown, however, 

 that if varieties of tomatoes which are normally red when ripe, 

 are ripened at high temperatures, 90 F. or above, their skins 

 will be yellow instead of red when fully ripe. Hence, the occur- 

 rence of carotin, or of lycopersicin, as the skin pigment is deter- 

 mined in part by the varietal character (being different in different 

 varieties when ripened at normal temperatures) and in part by the 

 temperature at which the fruit ripens. The two pigments are, 

 of course, isomers; but the difference in their structural arrange- 

 ment is not known. 



Fucoxanthin, C^H^Oe, is a brownish-red pigment, found in 

 fresh brown algae, and in some brown sea-weeds. Its formula 

 indicates that it is an oxidized carotin. With iodine, it forms a 

 compound having the formula C^H^OeLi. It is unlike carotin 

 and xanthophyll in that it has basic properties, forming salts 

 with acids, which are blue in color. 



PHYCOERYTHRIN AND PHYCOPttflEIN 



These are the principal pigments of red and brown seaweeds, 

 respectively. Their most characteristic difference from the 

 pigments of non-aquatic plants is that they are easily soluble in 

 water, and insoluble in most organic solvents, such as alcohol, 

 ether, etc. At first thought, this would appear to be impossible, 

 since the plants grow in water and it would seem that their water- 

 soluble pigments would be continuously dissolved out of the tis- 

 sues. The reason why this does not occur lies in the fact that 

 these pigments exist in the cells of the seaweeds in colloidal 



