342 Review of Hooker'* s Outlines 



4. In the post-pliocene period Greenland was either nnder 

 water, or if land quite as suitable as now for arctic plants. Most 

 probably it was in the latter case. Scandinavia had in that period 

 a much less advantage, if any, over Greenland in point of climate 

 than at present, and was probably connected with it by land or 

 chains of islands, while there is no reason to suppose that Green- 

 land was then connected with America. The flora of neither re- 

 gion could migrate to the south over the plains, because they 

 were submerged, unless indeed covered with that general glacier 

 which Agassiz at one time advocated, and Ramsay has recently 

 proposed to revive. That these plants migrated by means of drift 

 ice far to the south, there is good reason to believe ;^ but if they 

 were extirpated from their arctic homes, they could not have re- 

 turned in that way against the prevailing currents, nor could they 

 have returned over the emerged plains, which would have been 

 too warm and dry. They could have returned by only one agen- 

 cy, that of migratory birds, an agency which though not needed 

 for this purpose, has probably done much to give Lapland its rich 

 flora, as well as to scatter arctic plants to the south along certain 

 meridians. 



5. The law of distribution of arctic plants must always have 

 been different in America and the eastern continent, owing to the 

 north and south character of the coast lines and mountains in the 

 former, and the opposite arrangement in the latter, with the varied 

 effects of these diflerent arrangements on climates and on geolo- 

 gical subsidences and elevations. It could easily be shown that 

 this fact accounts for many apparent anomalies. 



6. It is farther to be observed that difierencc of geological for- 

 mation, and difference of soil as depending on this, constitute 

 great determining causes in the distribution of plants, as well as 

 in their variations. Until the botanical geographer pursues his 

 studies of distribution with a geological map in his hand, and a 

 knowledge of the habitudes of plants in reference to soils, his 

 labours will be to a great extent fruitless. A little more lime or 

 a little less alkali in the soil renders vast regions uninhabitable 

 by certain species of plants. For many of the plants of our Lau- 

 rentide hills to extend themselves over the calcareous plains south 

 of them, under any imaginable conditions of cHmate, is quite as 

 far beyond the range of possibility as to extend across the wide 

 ocean. A multitude of apparent anomalies belong to this cate- 



* See Can. Nat., April, 1862. 



