80 SECTIONAL ADDRESSES 
the case may be. The remainder show extraordinary little power of 
adaptability—a species here and there may do so, but not the bulk. ‘They 
quote H. H. Thomas *? ‘that there seems to be no indication in the geo- 
logical record of any gradual acclimatisation of the plants which existed 
in Eocene times in Europe as the Great Ice Age approached, and the 
climates became colder, and, presumably, also drier.’ As regards the 
flora they were studying—the London Clay flora—not a single genus 
that lived in Britain survived into Upper Pliocene times. They therefore 
conclude that the bulk character of a Tertiary flora does determine its 
climatic character, and that that of the London Clay zs sub-tropical. The 
presence of Nipa—the most northerly record so far—gives them a tempera- 
ture figure, and they ask both Simpson and Brooks whether they can 
supply such conditions in Britain. The temperature is that of a wet 
tropical forest—a lower figure than the normal tropical type—a mean 
annual temperature of 70° F. 
Simpson could only supply it by the aid of some measure of continental 
drift which Mrs. Reid and Miss Chandler could not accept. Brooks 
could only give that temperature with the aid of Simpson’s hypothesis 
of increased solar radiation, and increase of cloud and precipitation. But 
the plant evidence could be explained by Brooks’ hypothesis ; or, expressed 
otherwise, accepting plants as good indexes of climatic zones, an appro- 
priate zone temperature could be established in Britain during London 
Clay times by the application of a theory devised to explain glacial and 
non-glacial epochs. If further tests, from the distribution of other plants, 
were applied we might obtain sufficient information to determine which 
theory is the most satisfactory. Brooks’ hypothesis appeals to me because 
it does not demand increases in solar radiation over long periods. But 
increases for short periods I think are necessary to explain climatic 
rhythms that are known, and that can be traced back in the history of 
certain trees. I do not regard Brooks’ and Simpson’s theories as 
mutually exclusive, but as mutually complementary. 
FossiL PLANTS AND CLIMATIC RHYTHM. 
Recent researches in archeology in Africa and America, and also 
former discoveries in other parts of the world, have drawn attention to 
minor fluctuations in climatic character similar to those periodic cycles 
that meteorologists had also discovered from quite other considerations. 
Historical records, so far as they go, can be checked up; but these are 
of short duration from a geological standpoint. In regions of the world 
where trees had not been destroyed, either by man or other agencies, 
certain examples have reached a great age—several thousands of years ; 
and, if plants are good indexes of former conditions, here, if anywhere, is 
an opportunity to obtain a cross check on historical information, and a 
possible extension into pre-historic times. The work of Antevs®§ and 
A. E. Douglas®® on annual rings and their variation according to climatic 
57 “ Discussion on Geological Climates,’ Proc. Roy. Soc., 1930. 
58 Amer. Jour. Sc., vol. ix, p. 296 et seg. (1925). 
°° Carnegie Inst., Washington, vol. xi, no. 289 (1928). Brit. Assoc. Report, 
Bristol, p. 371 (1930). 
