202 Transactions of the Royal Microscopical Society. 
The position of these bands and also their general character 
will be better understood by means of Fig. 1. 
Fig. 1. — Spectra of Yellow Xanthophyll. 
In solid state . . 
In carbon bisulphide 
In absolute alcohol . . 
In Canada balsam . . 
700 
400 
In this and all the following drawings I do not give the spectra 
as they are seen with a prism, but as they would appear in an 
interference spectrum, in which the dispersion is in direct proportion 
to wave-lengths. This of course makes the red end much broader 
and the blue end much narrower than in the spectra usually 
observed. For convenience of reference I give the wave-lengths 
of a few Fraunhofer lines : 
A 7G0 D 589 F 486 G 430 
The change in the position of the bands often makes it easy to 
ascertain the condition in which a substance occurs in a living 
organism. For example, when yellow xanthophyll is dissolved in 
even a very small quantity of oil, the bands are at wave-lengths 
483 and 453, whereas, when it is in a free state, they are at 501 
and 469, and these differences show that in the petals of some 
yellow flowers like Gheliclonium majus it exists in the free state, 
though in the majority of cases it is dissolved in an oil. The 
spectra also show that in some flowers it is associated with wax or 
hard fat, in which it dissolves when warmed, but is set free on 
becoming cold and crystalline. 
The colouring matter of the red feathers of the Plantain eaters, 
described by Professor Church, and named by him turacine, is also 
an excellent illustration of the connection between the spectra of the 
solid substance and its solution, as will be seen from Fig. 2 and the 
