Il] FOSSIL PLANTS AND CLIMATE. 17 



perform feats of determination with hopelessly inadequate 

 specimens. Had this principle been generally followed, the 

 number of fossil plant species would be enormously reduced, 

 but the value of the records would be considerably raised. 



Our knowledge of plant anatomy, and of those laws of 

 growth which govern certain classes of plants to-day and in 

 past time, has been very materially widened and extended by 

 the facts revealed to us by the detailed study of Coal-Measure 

 species. The modern science of Plant Biology, refounded 

 by Charles Darwin, has thrown considerable light on the 

 laws of plant life, and it enables us to correlate structural 

 characteristics with physiological conditions of growth. Ap- 

 plying the knowledge gained from living plants to the study of 

 such extinct types as permit of close microscopic examination, 

 we may obtain a glimpse into the secrets of the botanical 

 binomics of Palaeozoic times. The wider questions of climatic 

 conditions depend very largely upon the evidence of fossil 

 botany for a rational solution. As an instance of the best 

 authenticated and most striking alternation in climatic con- 

 ditions in comparatively recent times, we may cite the glacial 

 period or Ice-Age. The existence of Arctic conditions has 

 been proved by purely geological evidence, but it receives 

 additional confirmation, and derives a wider importance from 

 the testimony of fossil plants. In rocks deposited before the 

 spread of ice from high northern latitudes, we find indubitable 

 proofs of a widely distributed subtropical flora in Central and 

 Northern Europe. Passing from these rocks to more recent 

 beds there are found indications of a fall in temperature, and 

 such northern plants as the dwarf Birch, the Arctic Willow 

 and others reveal the southern extension of Arctic cold to our 

 own latitudes. 



The distribution of plants in time, that is the range of 

 classes, families, genera and species of plants through the 

 series of strata which make up the crust of the earth, is a 

 matter of primary importance from a botanical as well as from 

 a geological point of view. 



Among the earlier writers, Brongniart recognised the marked 

 differences between the earlier and later floras, and attempted 

 s. 2 



