i867— 1882] EVOLUTION OF ANGIOSPERMS 21 



mystery. Certainly it would be a great step if \vc could Letter 395 

 believe that the higher plants at first could live only at a high 

 level; but until it is experimentally [proved] that Cycadeae, 



ferns, etc., can withstand much more carbonic acid than the. 

 higher plants, the hypothesis seems to me far too rash. 

 Saporta believes that there was an astonishingly rapid 

 development of the high plants, as soon [as] flower-frequent- 

 ing insects were developed and favoured intercrossing. I 

 should like to see this whole problem solved. I have fancied 



avoid it. Ball draws attention to the imperfection of our plant records 

 as regards the floras of mountain regions. It is, he thinks, conceivable 

 that there existed a vegetation on the Carboniferous mountains of which 

 no traces have been preserved in the rocks. See Fossil Plants as Tests 

 of Climate, p. 40, A. C. Seward, 1892. 



Since the first part of this note was written, a paper has been read 

 (May 29th, 1902) by Dr. H. T. Brown and Mr. F. Escombe, before the 

 Royal Society on "The Influence of varying amounts of Carbon Dioxide 

 in the Air on the Photosynthetic Process of Leaves, and on the Mode of 

 Growth of Plants. 1 ' The author's experiments included the cultivation 

 of several dicotyledonous plants in an atmosphere containing in one case 

 180 to 200 times the normal amount of CO., and in another between 

 three and four times the normal amount. The general results were 

 practically identical in the two sets of experiments. " All the species 

 of flowering plants, which have been the subject of experiment, appear 

 to be accurately 'tuned' to an atmospheric environment of three parts 

 of CO. per 10,000, and the response which they make to slight increases 

 in this amount are in a direction altogether unfavourable to their growth 

 and reproduction." The assimilation of carbon increases with the increase 

 in the partial pressure of the CO._. But there seems to be a disturbance 

 in metabolism, and the plants fail to take advantage of the increased 

 supply of CO.,. The authors say : — " All we are justified in concluding 

 is, that if such atmospheric variations have occurred since the advent of 

 flowering plants, they must have taken place so slowly as never to outrun 

 the possible adaptation of the plants to their changing conditio'.. 



Prof. Farmer and Mr. S. E. Chandler gave an account, at the same 

 meeting of the Royal Society, of their work "On the Influence of an 

 Excess of Carbon Dioxide in the Air on the Form and Internal Structure 

 of Plants." The results obtained were described as differing in a remark- 

 able way from those pieviously recorded by Teodoresco \Rr,\ Gen. 

 Botaniqut, II., 1899). 



It is hoped that Dr. Horace Brown and Mr. Escombe will extend 

 their experiments to Vascular Cryptogams, and thus obtain evidence 

 bearing more directly upon the question of an increased amount of CO 1 

 in the atmosphere of the Coal-period forests. 



