198 THE HAUNTS OF LIFE 



the possible seeds are to become real seeds 

 which will sprout. And even when the pollen 

 can pass from the stamens of the flower to the 

 pistil of the same flower (self-pollination), 

 the results are not usually so good as when 

 the pollen is carried by insects (or by the 

 wind) from one blossom to another. When 

 there is cross-fertilisation the yield of seeds is 

 better. And the plants so produced tend to 

 be more variable, which will be a good thing 

 if it is useful for the plant to change. 



The Third Great Invasion. It was about 

 the end of the time known as the Devonian 

 or Old Red Sandstone that amphibians made 

 their appearance, and, in the next age, the 

 Carboniferous, when the coal measures were 

 laid down, they had their golden age. These 

 early amphibians, ancestors of our frogs and 

 toads, newts and salamanders, were the ad- 

 vance guard of the third great invasion, which 

 eventually led to the appearance of reptiles, 

 birds, and mammals. This third invasion 

 meant the opening up of many new possibili- 

 ties for animals, and, in the long run, it led 

 to man. 



It is interesting to notice some of the new' 

 things that began with amphibians, the ad- 



