General 



because there is no recognised translation of the German 

 term " Urboden/' which means land or soil which has 

 never been touched or altered by plants). 



In making a tunnel near Glasgow, a layer of almost 

 liquid clay had been struck. On a field close by the 

 ordinary surface soil had been removed from a few 

 square yards and piled up in a long mound, and the 

 whitish clay which had been buried deep in the earth 

 since some time in the ice age was deposited on the 

 vacant space. 



After the work had been stopped, there was an 

 extraordinary difference between the flowers on the 

 mound of surface soil and those of the " mineral " clay. 

 During two summers scarcely a plant succeeded in 

 establishing itself on the clay, and those few that did 

 manage to grow did so unhappily and seemed also to 

 depend chiefly upon blown dust or accidental patches of 

 good earth. On the mounds of surface soil the weeds 

 and grasses were extremely luxuriant, and produced a 

 rich and flourishing crop in a very short time. 



A freshly cooled lava flow is perhaps the only modern 

 representative of what was the condition of the whole 

 world before plants had begun to colonise its surface. 

 The manner in which such fresh lavas are gradually 

 occupied by vegetation is extremely interesting, because 

 this process gives us some hint as to how, in the very 

 earliest of all geological periods, the plant-world may 

 have set about its task. 



The eruption of Krakatoa gave a splendid opportunity 

 for such observations ; an entirely clean sweep had been 

 made of all living plants and animals : the soil was 

 nothing but newly cooled lavas or volcanic ash. 



Dr. Treub found that the first vegetation consisted of 

 certain minute blue-green seaweeds. Next came a pro- 

 fusion of ferns, and at a later date especially such flower- 



19 



