268 THE GEOLOGICAL HISTORY OF PLANTS. 



beyond what a fair study of our material may warrant, 

 or to infer that such primitive types must necessarily 

 have been of low grade, or that progress in yarietal forms 

 has always been upward. The occurrence of such an 

 advanced and specialised type as that of Dadoxylon 

 in the Middle Devonian should guard us against these 

 errors. The creative process may have been applicable 

 to the highest as well as to the lowest forms, and subse- 

 quent deviations must have included degradation as well 

 as elevation. I can conceive nothing more unreasonable 

 than the statement sometimes made that it is illogical or 

 even absurd to suppose that highly organised beings 

 could have been produced except by derivation from pre- 

 viously existing organisms. This is begging the whole 

 question at issue, depriving science of a noble department 

 of inquiry on which it has as yet barely entered, and an- 

 ticipating by unwarranted assertions conclusions which 

 may perhaps suddenly dawn upon us through the inspira- 

 tion of some great intellect, or may for generations to 

 come baffle the united exertions of all the earnest pro- 

 moters of natural science. Our present attitude should 

 not be that of dogmatists, but that of patient workers 

 content to labour for a harvest of grand generalisations 

 which may not come till we have passed away, but which, 

 if we are earnest and true to Nature and its Creator, may 

 reward even some of us. 



Within the human period great changes of distribu- 

 tion of plants have occurred, chiefly through the agency 

 of man himself, and we have had ample evidence that 

 plants are able to establish themselves and prosper in 

 climates and conditions to which unaided they could not 

 have transported themselves, as, for instance, in the case 

 of European weeds naturalised in Australia and New Zea- 

 land. There is, however, no reason to believe that any 

 specific change has occurred to any plant within the Pleis- 

 tocene or modern period. 



