Flora and Vegetation of Westei-n Canada. 19 



growth and wood margins are rich in shrubs, Corni (including 

 the beautiful dwarf C. canadensis, with its brilliant crimson 

 beriies), guelder roses, elders, &c. 



The vastly greater number of species of trees in Eastern 

 America strikes a stranger. In Europe not more than a dozen 

 or twenty species of trees would be met with in an ordinary 

 ramble, but in America three or four times that number might 

 be observed. The explanation of this fact is connected with the 

 oscillations of temperature and climate, to which the world has 

 been subjected. In glacial periods the trees were driven south- 

 ward, both in the Old World and the New ; but when a warmer 

 era set in, in the former, the Mediterranean in Europe, and the 

 mountain ranges running from east to west in Asia, presented 

 an impassable barrier to their return northward ; whilst in 

 America, the mountain ranges all runnmg north to south, no 

 such obstacles existed, and they readily followed the warmer 

 wave northwards again, so that we have not only all the hardier 

 northern forms and families, but a vast number of southern and 

 semi-tropical ones. 



The herbaceous flora of forest regions is always poor both in 

 species and individuals ; hence, when the land is cleared, as a 

 large portion of the eastern states of the Union and of the 

 Dominion was, by forest fires during the Indian occupation, and 

 later by the settler, a floral vacuum residted (as Prof. Asa Gray 

 well describes it), and to fill this, northern, southern, and to a 

 large extent mtroduced foreign plants rushed in ; hence we 

 have here, in the main, a derivative, non-indigenous flora, and 

 we see a vast nimiber of the most familiar weeds of the Old 

 World flourishing in abnormal vigour. The mullein, the com- 

 mon plantain, and many of our most famihar garden pests, thus 

 everywhere abound. 



Passing westward beyond the lakes to the great prairies, con- 

 sisting largely of rich alluvium resting on cretaceous clays, we 

 have an entirely distinct and thoroughly indigenous flora, 

 presenting in spring and early summer a carpet of brilliant and 

 beautiful flowers. Leguminous plants, especially species of Astra- 

 galus, Petalostcmon, Lupinus, and Lathy rus ; Composites, of the 

 great American genus Aster, SoHdagos or golden-rods, Erigerons, 

 — which in America replace our ragworts (Senecio), and hawk- 

 weeds (Hieracium), — Gaillardias and Rudbeckias ; and (Enotheras, 

 or evening primroses, are the most striking features. 



This flora is of interest as containing so large a number of 

 plants, recently introduced into our gardens, among the now 

 fashionable " hardy perennials." Some, however, such as 

 species of Aster (Michaelmas daisies), golden-rods, and sun- 

 flowers, are among the oldest denizens of our gardens. 



The tree flora of the prairies is extremely meagre ; chiefly 



