144 REPORTS ON THE STATE OF SCIENCE.—1913. 
ment of Plants. By F. Keeble and E. F. Armstrong [in the ‘ Journal 
of Genetics ’]. 
(f) The Formation of the Anthocyan Pigments of Plants. IV. The 
Chromogens. By F. Keeble, E. F. Armstrong, and W. N. Jones. 
(g) The Formation of the Anthocyan Pigments of Plants. V. The 
Chromogens of White Flowers. By W. N. Jones. 
(h) The Formation of the Anthocyan Pigments of Plants. VI. By 
F. Keeble, E. F. Armstrong, and W. N. Jones. 
Considerable progress has been made in elucidating the part played 
by oxidising catalysts in the production of plant pigments. By means 
of suitable agents—in particular benzidine and a-naphthol—oxydases 
and peroxydases can be localised in plants both in the flower petals 
and in the vegetative parts. Evidence has been accumulated in favour 
of the hypothesis that the soluble sap pigments of plants are formed 
by the oxidation of a colourless chromogen through the agency of an 
oxydase. The method has been applied with success to certain pro- 
blems in genetics. 
The sap pigment may be reduced to the colourless chromogen by 
the agency of a reducing substance. Such a change takes place when 
the coloured cell is stimulated by a hormone (a substance which pene- 
trates the cell membrane) under conditions in which the amount of 
water present is a minimum. When the conditions are reversed and 
there is an excess of water in the system, the chromogen is reoxidised. 
Both the reducing substance and the reduced pigment are soluble in 
aqueous alcohol of a suitable strength (90 per cent.). After extraction 
of a coloured petal by alcohol of this strength, both the solution and 
the extracted petal are colourless; but they can be caused to recover 
their original colour—the solution on evaporation of the alcohol 
and dissolution of the residue in water, the petal on warming in 
water. There is evidence that the flower contains an excess of 
chromogen beyond that normally converted into pigment. The 
reducing substance is not destroyed by boiling: it cannot therefore 
be classed as an enzyme. The experiments afford proof of the exist- 
ence of an oxidising-reducing mechanism in the cell sap which controls 
the formation of flower colour and is itself regulated by the condition of 
concentration of the cell sap. Dilution favours oxidation, concentra- 
tion alters the balance in the opposite direction. 
Very little progress has yet been made in determining the chemical 
nature of the sap pigments. The researches of A. G. Perkin have made 
it almost certain that the soluble yellow pigments belong to the class of 
hydroxyflavones of which quercetin is the best known representative. 
On genetical grounds there is strong evidence in favour of regarding 
these yellow pigments as antecedents of the red, magenta, and blue sap 
pigments. By hydrolysis and subsequent reduction and oxidation or by 
hydrolysis and oxidation, red pigments have been obtained from a 
number of yellow flowers, such, for example, as the wallflower, daffodil, 
and primrose; it is possible that the coloured varieties of these species 
may arise in a similar manner. 
The most fruitful discovery during the year has been the proof 
afforded by Chodat that the action of tyrosinase on an amino- acid, 
