664 REPORT—1899. 
SECTION B.—CHEMISTRY. 
PRESIDENT OF THE SEcTION—Horacz T. Brown, LL.D., F.RS. 
THURSDAY, SEPTEMBER lA. 
The President delivered the following Address :— 
THE subject which I have chosen for my Address is the fixation of carbon by 
plants, one which is the common meeting-ground of Chemistry, Physics, and 
Biology. I must, however, confine myself only to certain aspects of the question, 
since it is manifestly impossible to fully discuss the whole of a subject of such 
magnitude and importance within the time at my disposal. 
We have become so accustomed to the idea that the higher plants derive the 
whole of their carbon from atmospheric sources that we are apt to forget how very 
indirect is the nature of much of the experimental evidence on which this belief is 
founded. There can, of course, be no doubt that the primary source of the organic 
carbon of the soil, and of the plants growing on it, is the atmosphere; but of late 
years there has been such an accumulation of evidence tending to show that the 
higher plants are capable of being nourished by the direct application of a great. 
variety of ready-formed organic compounds, that we are justified in demanding 
further proof that the stores of organic substances in the soil must necessarily be 
oxidised down to the lowest possible point before their carbon is once more in @ 
fit state to be assimilated. 
It was the hope of gaining more direct evidence on this important question 
which led me some time ago to attack the problem experimentally in conjunction 
with Mr. F. Escombe, the resources of the Jodrell Laboratory at Kew having 
been kindly put at our disposal by Sir W. Thiselton-Dyer and Dr. D. H. Scott. 
Up to the present time our experiments have not been carried far enough to enable 
us to give a positive answer to the main question, but they have already suggested 
a new method of attack which will enable usin the future to determine, with a 
fair amount of certainty, whether any particular plant, growing under perfectly 
natural conditions, derives any appreciable portion of its carbon from any other 
source than the gaseous carbon dioxide of the atmosphere. 
During the course of the inquiry, many interesting side issues have been raised 
which we believe to be of some importance in their bearing on the processes of 
plant nutrition, and it is to a consideration of these that I intend to devote the 
greater part of my Address, 
I must, however, in the first place indulge in a little historical retrospect, and 
am the more tempted to do this, as far as the early pioneers in this branch of 
Imowledge are concerned, since a critical study of their writings has shown me 
very clearly that the relative merits of some of these older workers, and the re- 
spective parts which they took in founding the true theory of assimilation, have in 
our own time been much misrepresented by more than one historian of science 
whose name carries great weight. 
