204 ROUND THE YEAR 



correctly called the Aloe) of Mexico has spread 

 through the tropics, and has established itself on the 

 shores of the Mediterranean, but it cannot hold its 

 own except in spots where our common weeds refuse 

 to grow or grow at a disadvantage. I know of not a 

 single animal native to a distant southern country 

 which can maintain itself in Europe. 



Hooker and Wallace have spoken of the aggressive- 

 ness and colonising power of the Scandinavian flora, 

 but this is too limited an expression. The plants, 

 and not only the plants but the animals of Europe 

 and the greater part of Asia exhibit this dominance ; 

 it is a feature of the Palaearctic fauna and flora. The 

 fauna and flora of North America occasionally give 

 way to the Palaearctic fauna and flora, but show 

 dominance over the animals and plants of other parts 

 of the world. What is known of the animal life of 

 the more recent geological periods tends to show that 

 this relation is of very long standing. Not a few 

 animals now characteristic of distant countries, such 

 as the Lemurs, Tapirs, Hippopotamus, Giraffe, 

 Sea-cows, Sloths, Elephants and Marsupials, were 

 once European. There is, I believe, nothing to 

 show that they did not originate in the northern 

 hemisphere. But the imperfection of the geological 

 record bids us to be careful in drawing wide 

 inferences. 



The plants and animals of our fresh waters do not 

 enjoy the same dominance. Our fresh waters are cut 

 up into many small portions, and the severity of the 

 competition in them is thereby greatly reduced. 

 Accordingly we find. that many of our fresh-water 





