226 
chlorophyll may, in some cases, pass into xanthophyll by 
oxidization, and xanthophyll into chlorophyll by deoxidiza- 
tion; but neither point can be considered to be established. 
Chlorophyll, when dissolved, jis oxidized with considerable 
difficulty. On adding a little bromine to its alcoholic solu- 
tion, it is first changed into an orange-yellow colour, which 
gives a spectrum with a dark absorption-band in the green, 
and perhaps this compound is changed by more bromine into 
a yellow colour, cutting off the blue end of the spectrum, 
with no well-marked bands, and is made colourless by further 
change. These products have strong analogy with xantho- 
phyll, but do not actually correspond with it. Perhaps this 
is scarcely likely, for it is at once decomposed and rendered 
colourless by such powerful oxidizing processes as can change 
chlorophyll. Still, as far as they go, they show that chloro- 
phyll can be converted by oxidization into yellow colours, 
corresponding, in many particulars, with xanthophyll. 
Judging from what occurs in the leaves themselves, high 
vitality, and a strong light, are more essential for the produc- 
tion of chlorophyll than for that of xanthophyll, and hence 
not only do leaves become deeper green by continued ex- 
posure to light, but some tender variegated plants lose that 
character when kept at a temperature more favorable to their 
growth. The production of an abnormally large amount of 
xanthophyll seems, therefore, to indicate low vitality. When 
certain leaves rapidly change from green to red, it appears 
very much as though erythrophyll could be derived from the 
chlorophyll by some direct and simple alteration. ‘There is 
no doubt that this change of colour is often accompanied 
with the disappearance of the greater part of the chlorophyll, 
as may be seen by examining the spectrum of the light 
transmitted by the leaves themselves ; but by digesting them 
in water containing sulphite of soda and citric acid, so as to 
remove the red colour, it is easy to see that they are of the same 
yellow colour as if they had faded without having turned red. 
Moreover, in many cases much erythrophyll is developed 
when the amount of chlorophyll is but slightly diminished, 
and thus it could scarcely have been due to any simple 
change of the latter. This conclusion is also supported by 
the fact that no substance analogous to erythrophyll is pro- 
duced by the artificial oxidization of chlorophyll. There is, 
however, certainly a connection of some kind ; for when ery- 
throphyll is developed in patches in young leaves, there is 
usually a decided deficiency in the amount of chlorophyll in 
those parts, as shown by the spectrum of transmitted light. 
In the present state of our knowledge it appears as though 
