246 Ingvar Jorgensen and Walter Stiles. 
is mixed with accompanying oils, waxes, etc., but petrol-ether does 
not extract at all from dried leaves, so it is feasible to suppose that 
the chlorophyll in the chloroplast is in the colloidal condition, that 
water added to the pure organic solvents dissolves the mineral 
substances in the leaf, and the salt solution so formed alters the 
colloidal condition of chlorophyll in the chloroplast and makes it 
easily soluble. 
In this connection it should be pointed out that the pureorganic 
solvents can extract the chlorophyll from fresh leaves, as there is of 
course, abundant water present in them. 
Support for this assumption is given by the fact that colloidal 
solutions of chlorophyll in water made up from the pure extracted 
pigment behave in a similar way to the dried leaf powder. Thus if 
a colloidal solution of chlorophyll is mixed with ether, the ether 
remains colourless, hut if a little salt solution, for instance, a solution 
of calcium chloride or calcium nitrate, is added, on shaking the 
ethereal layer becomes coloured green. The salt solution has 
precipitated some of the chlorophyll from its colloidal condition and 
it is now easily soluble in ether. 
In regard to the actual state of chlorophyll in the leaf there has 
been some difference of opinion. Arnaud (1885) supposed 
that capillary forces kept the chlorophyll hack in the leaf, and 
Willstatter himself at one time assumed that chlorophyll in the 
leaf was present in the form of adsorption compounds with colloids. 
Similarly Tswett (1901) held that the pigment was bound to the 
skeleton of the chloroplast by molecular adsorption. Recently 
Palladin (1910a, 1910b) suggested that the chlorophyll is present in 
the leaf in a state of chemical combination, particularly with the 
so-called lipoid substances, and he shows that the use of solvents for 
extraction could be explained by their dissociating power in regard 
to the adsorption compound. 
Willstatter’s present opinion is that the chlorophyll in the 
chloroplast is present in a colloidal mixture, and there appears to 
he a good deal of experimental evidence in support of this view, even 
if it may have to he slightly modified when we have more experi¬ 
mental knowledge of the kinetics of the physiological processes 
involved. 
We may mention briefly some other reasons for the assumption 
that chlorophyll is present in the colloidal condition. There is first 
evidence derived from spectroscopic examination. According to 
Tswett (1910) and other writers the absorption bands in the spectrum 
of the living leaf are displaced towards the red end of the spectrum 
as compared with the bands in the spectrum of extracted chloro- 
