1899] SCIENTIFIC EXPLANATIONS 251 



learning of how many, or rather of how few, different kinds of thread 

 it is woven, finding how each separate thread enters into the pattern, 

 and seeking from the pattern woven in the past to know the pattern 

 yet to come." . . . We have heard from unfriendly critics much in 

 regard to the dogmatism of science ; it is time rather to speak of its 

 modesty. 



Ail Unsolved Problem. 



In his opening address to the Chemical Section of the British Associa- 

 tion, Dr. Horace T. Brown not unnaturally took for his subject the 

 fixation of carbon by plants, a problem towards the solution of which 

 he has himself made some notable contributions. The address is a 

 fine illustration of the true scientific temper, and of the value to 

 biologists of co-operation with workers in chemistry and physics. 

 Definite results are still far to seek, but the address indicates a hopeful 

 outlook, and it also impresses us anew with the danger of hard and 

 fast statements, and with the incipient character of vegetable physiology. 



The president of Section B began by pointing out that although 

 we cease not to impress upon our students that the higher plants 

 derive the whole of their carbon from atmospheric sources, the experi- 

 mental evidence for this hard and fast statement is very indirect. 

 " 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 a fit state to be assimilated." Along with Mr. F. Escombe, 

 Dr. Brown has been recently experimenting in order if possible to reach 

 some satisfactory answer to this important question. " Up to the 

 present time," he says, " 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 us in 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." 



The address contains a valuable critical account of what has been 

 done in the past, and we venture to quote the summing-up. It does 

 not sound altogether encouraging, but there is no object in blinking 

 the facts. " The brilliant discoveries of recent years on the constitu- 

 tion and synthesis of the carbohydrates have not brought us sensibly 



