THE TERTIARY TO THE MODERN PERIOD. 235 



The Bermudas, altogether recent islands, have one hun- 

 dred and fifty species of native plants, all of which are 

 West Indian and American, and must have been intro- 

 duced by the sea-currents or by migratory birds. 



And so the earth became fitted for the residence of 

 modern man. Yet it is not so good or Edenic a world as 

 it once was, or as it may yet become, were another revo- 

 lution to restore a mild climate to the arctic regions, and 

 to send down a new swarm of migratory species to renew 

 the face of the earth and restore it to its pristine fertility 

 of vegetable life. 



Thus closes this long history of the succession of 

 plants, reaching from the far back Laurentian to the 

 present day. It has, no doubt, many breaks, and much 

 remains to be discovered. Yet it may lead us to some 

 positive conclusions regarding the laws of the introduction 

 of plants. 



One of these, and perhaps the most remarkable of all, 

 is that certain principles were settled very far back, and 

 have remained ever since. We have seen that in the 

 earliest geological periods all that pertains to the struct- 

 ure, powers, and laws of the vegetable cell was already 

 fixed and settled. When we consider how much this 

 implies of mechanical structure and chemical and vital 

 property, the profound significance of this statement be- 

 comes apparent. The relations in these respects between 

 the living cell and the soil, the atmosphere and the sun- 

 shine, were apparently as perfect in the early Palaeozoic 

 as in any subsequent time. The same may be said of the 

 structures of the leaf and of the stem. In such old forms 

 as Nematophyton these were, it is true, peculiar and rudi- 

 mentary, but in the Devonian and Carboniferous the 

 structure of leaves and stems embodied all the parts and 

 principles that we find at present. In regard to fructifi- 

 cation there has been more progress, for, so far as we 

 know, the highest and most complex forms of flowers, 



