654 The Outline of Science 



independence." The infection of the heather seems to take place 

 shortly after the germination of the seeds, and it is a remarkable 

 fact that the seedlings do not develop roots in a pure sterilised 

 culture where there is no partner-fungus. But infection with the 

 right fungus brings about normal development. The heather's 

 health and continuance depend on its symbiosis with a Fungus. 

 More information in regard to these partnerships will be found in 

 the article on BOTANY. 



3 



Man and the Web of Life 



If the world of living creatures is a vast interlinked system 

 the fact must be carefully appreciated by everyone who would 

 operate on Animate Nature, and that is what Man is always 

 doing. If he is to control Nature, he must first know and then 

 respect the web of life. By ignoring it or defying it, Man has 

 brought much trouble upon the earth. Let us consider some 

 illustrations of his mistakes and of his achievements. 



1. Man is a distributor of plants and animals. About 1860 

 he took rabbits to Australia, and there, in the absence of their 

 natural enemies, these adaptable creatures (though they will not 

 take to Ireland) multiplied excessively and turned vast areas of 

 fertile country into barren desert. Over a dozen times the Euro- 

 pean sparrow was introduced into the United States, partly in 

 the hope of checking the elm-tree caterpillars. This it did in some 

 measure, but only to become itself a greater pest, doing much 

 damage to the crops and driving away native insectivorous birds. 

 The annual cost to the States amounts to a prodigious sum. 



Of course, man is not always doing such stupid things. He 

 imports fruit-trees into South Africa and wheat into America; he 

 establishes turkeys from Mexico in Europe and sheep from Scot- 

 land in New Zealand. It must be noted, however, that his suc- 

 cesses have been greatest with domesticated animals and cultivated 

 plants, over which he had previously established some control. 



