102 THE WORLD OF LIFE 



dinarj variations of soil, we have to take account of the effects 

 of diversity of treatment as meadows, pasture, or fallow land, 

 each resulting in a characteristic grouping of species easily 

 recognisable over wide areas. In pasture land each kind 

 of domestic animal leads to the presence or absence of certain 

 species, while in the vicinity of farms or villages, the presence 

 of geese, pigs, or poultry has a distinctive influence. 



What a new light these researches throw upon the develop- 

 ment of the vegetation of each country during past ages ! We 

 see how the indigenous vegetation of oceanic islands, in the 

 total absence of mammalia, must have gradually eliminated 

 some of the chance immigrants by which they were first 

 stocked, and favoured others often of later date, and how, in 

 the com^^etition with each other, those species which were most 

 easily modified into a shrubby or arboreal type would have the 

 advantage. Thus may we explain the composites, lobelias, 

 violets, and plantains of the Sandwich Islands being mostly 

 shrubs or even trees of considerable size, and so abundant in 

 species as to form a characteristic feature of the vegetation. 

 Numerous Caryophyllacese, Primulacese, and a Geranium are 

 also shrubs or small trees. In the Azores a Campanula and 

 a Sempervivum are shrubs. 



Again, the knowledge we have recently gained of the won- 

 derfully rich mammalian fauna of temperate Xorth America 

 in middle and late Tertiarv times — camels, ancestral horses 

 and cattle, mastodons, and many others, which disappeared 

 at the on-coming of the glacial epoch — affords us a very im- 

 portant clue to the development of its special vegetation. 

 Every change of animal life that so often occurred in all the 

 continents — the union and separation of the sub-arctic lands 

 at various epochs, the temporary separation of Xorth and South 

 America in late Tertiarv times, and that of Africa from 

 Europe and Asia during the Early and Middle Tertiary — 

 must all have profoundly affected the special developments 

 of the vegetation, as well as of the animal life, in the respec- 

 tive areas. 



