THE EVOLUTION OF THE PLANT- WORLD 13 



CHAPTER III 



THE TIME AND PLACE OF THE ORIGIN OF 

 PLANT-LIFE 



WE know little, or nothing, as to the period of the origin 

 of plant-life. 



Among the oldest rocks that are probably of sedi- 

 mentary origin, the Laurentian of Canada, there occur 

 beds of graphite, or mineral carbon, destitute of all 

 organic structure, which may be of vegetable origin. 

 In more modern strata, still of immeasurable antiquity, 

 the Cambrian, ripple-marks, the tracks of animals, and 

 crystalline layers recalling the " frost trees " of our 

 window-panes have been erroneously described as sea- 

 weeds. In the later Ordovian and Silurian series more 

 precisely recognisable traces of Algae are found, some of 

 considerable size and of comparatively advanced organ- 

 isation, suggesting that among marine plants, as among 

 land plants, which make their first appearance in the 

 Devonian period, a long evolutionary history has been 

 lost in the metamorphosed rocks of preceding ages. That 

 the earliest known fossil plants, and, in fact, all those 

 certainly older than the Devonian period, are Algae may 

 be owing to our knowledge of the sedimentary rocks of 

 those early ages being confined to marine deposits. It 

 agrees, however, with much evidence, derived from 

 structure, pointing to that group as the first to be 

 evolved in the history of the plant- world. As it has 

 been suggested that animal life originated in shallow 

 sea-water near shore, so, perhaps, did that plant life 

 which most probably had its beginning about the same 

 time as, or somewhat before, the animal world. 



We have as little definite knowledge with regard to 

 the place of origin of the plant -world as we have with 

 reference to its period. The brilliant suggestion of 

 Buffon that the earth in cooling would cool first at its 

 poles, and that life, therefore, probably originated 

 at the North Pole, and then migrated southward in 

 successive dispersing hordes, belongs to a time when it 

 was not realised that the origin of life dated back to a 

 remote past with a distribution of land and water very 



