210 TILLEKS OF THE GROUND CHAP. 



ments, for in some of these the sand in which the 

 plants were grown was so treated that it could not 

 be supposed to contain living bacteria. In the 

 Rothamsted experiments also, the sand was carefully 

 sterilised, that is, any bacteria present were killed 

 before the experiment began. 



Berthelot made some other suggestions and 

 performed some experiments which helped to throw 

 light upon the problem, though they did not solve 

 it. He died, it may be mentioned, in 1907, and 

 was one of the last of the great scientific men of 

 the middle of the nineteenth century. Many tales 

 might be told of him, but for these we have no 

 space now, no space even to tell of the dignity 

 with which at the last he laid down his finished 

 task, and entered into rest. That is, however, a 

 story which is well worth reading. 



Going back to the nitrogen problem, we find 

 that when Berthelot had made the suggestion 

 about the bacteria the answer was nearly found, 

 though it was ten more years before it was finally 

 given. 



In 1886, a German man of science named 

 Hellriegel read at a meeting in Berlin a paper on a 

 long series of experiments which he had performed. 

 These experiments gave the following results. 

 Clover, peas, beans, and other plants of the Pea 

 family have usually on the roots little nodules 



