g6 Ingvar Jorgensen and Walter Stiles. 
land plants to be a mixture of four substances, two green and two 
yellow, all possessing highly distinctive optical properties. The 
green substances yield solutions exhibiting a strong red fluorescence, 
the yellow substances do not. The four substances are soluble in 
the same solvents and three of them are extremely easily decomposed 
by acids or even acid salts, such as bis-oxalate of potash, but by 
proper treatment each may he obtained in a state of very approxi¬ 
mate isolation so far at least as coloured substances are concerned.” 
Although it is a matter of national pride that the discovery of 
the four leaf pigments should have been made by a British worker, 
yet on the other hand the almost complete neglect with which 
later investigators in this country have treated Stokes’ work is 
certainly very discreditable. When the obsession for demonstrating 
the presence of formaldehyde in the leaf (started by Baeyer’s 
hypothesis in 1870, and first ‘experimentally’ investigated by 
Pollacci in 1902), began in this country with the work of Usher 
and Priestley in 1906, these writers neglected the presence of two 
green pigments and completely left out of consideration the yellow 
pigments in their theory of carbon assimilation. How much of the 
recent inconsequent work on the same subject might have been 
avoided if all these later writers had been aware of, and taken notice 
of, the work of Stokes. 
Again, the extraction and separation of the pigments without 
the aid of chemical action is due to Stokes. In a paper in the 
Journal of the Chemical Society for 1864, he says “ For convenience 
and rapidity of manipulation, especially in the examination of very 
minute quantities, there is no method of separation equal to that 
of partition between solvents which separate after agitation. 
Bisulphide of carbon in conjunction with alcohol enabled the 
lecturer to disentangle the coloured substances which are mixed 
together in the green colouring matter of leaves.” 
The use of nettle leaves for extraction of chlorophyll was also 
recommended by Stokes in a paper published in Transactions of 
the Royal Society in 1852. 
Considering that these observations were only side issues of 
Stokes’ work, it is very remarkable that they should have been so 
correct. There can he no doubt that he did a great deal more 
work on chlorophyll than appears from his published work. He 
announced his intention of publishing work on chlorophyll, but it 
never appeared, and apparently nothing has so far been found 
among his papers referring in detail to these investigations. 
(To be continued). 
