188 H. B. GUPPY, M.B.^ F.E.S.E., ON PLANT-DISTI^IBUTION 



the story of Genesis, and whilst seer and bard in all ages have 

 made it their theme the man of science has not been able to 

 disprove it. We may differ as to the details connected witli 

 the emergence and building up of the continents ; but geologists 

 seem generally agreed that in the process of time the land 

 surface has become less insular and more continental (Sir A. 

 Oeikie, in Encycl. Brit., xxviii, 635), that indeed the continents 

 •originated as islands, which have become united through succes- 

 sive movements of emergence, or, to put it brieHy, that the 

 continents have grown w^itli tlie ages. We remember how Suess 

 and other geologists emphasise the view that the great land- 

 masses possess in each case a region wldch, since palieozoic 

 times, has never been submerged and has served as the nucleus 

 for tlie growth of each continent. 



We get on somewdiat firmer ground when we come to the 

 differentiation of the life-conditions that finds its expression 

 chiefly in tlie diversification of climate. With the cooling of 

 the earth and the emergence of the land the uniformity of life- 

 conditions began to pass away, and climates as such commenced 

 to develop. There is, however, an important preliminary 

 consideration to be borne in mind. Climatic changes during 

 the secular cooling of the earth would assume a double character. 

 There would be the general alterations affecting the whole 

 globe, and there would be the more localised changes marking 

 <3limatic differentiation. The first would be concerned with 

 the general lowering of temperature, the decrease in humidity, 

 the increased influence of the sun's rays, and the development 

 •of the seasons. The second would be concerned with the 

 climatic characteristics of each region or locality. Whilst the 

 earth's climate has, generally speaking, been getting cooler, 

 drier and more sunny, it has also become infinitely more 

 diversified. 



Now in the response made by plants to the changes of 

 climate, or to the conditions of existence determined by them, we 

 ought to be able to distinguish two corresponding sets of effects, 

 •one characterising plants in general, and corresponding to the 

 secular change of climate over all the earth, the other concerned 

 with localised associations of plants, and connected with the 

 diversification of climates in individual regions. Such effects 

 would have nothing to do with the development of the great, 

 classes of plants. I'he moss, the fern, and the flowering plant 

 ' would in each case display in its characters the double impress. 



The response to the (jcneral chavfjr in tlie earth's climatic 

 conditions would be denoted by some change that plants of all 



