Earlv Observations 



209 



'r\iii.K K>. ( 'uoi'-Korv ri<)\ Kxphuimknt hk Uoissinc; aii/i 



Boussingault made an effort to repeat these experiments under more 

 carefully controlled conditions. He ignited the sand, thereby killing 

 the bacteria, and found that neither cereals nor legumes were capable 

 of assimilating nitrogen from the atmosphere. 



The German chemist Liebig (1843) could not accept the idea that 

 atmospheric nitrogen can be assimilated by plants. The beneficial 

 effects of leguminous plants were explained by the fact that the 

 plants form a large leaf surface and thus expose a greater area for 

 absorption of ammonia from the atmosphere. The results of Bous- 

 singault's rotation experiments, which occupied sixteen years, were 

 considered to be due to errors in the analysis of the manure. Since 

 the farm manure was dried in a vacuum at 110°C before being 

 analyzed for nitrogen, at least half the ammonia nitrogen could have 

 been volatilized. Liebig suggested that, had such errors been taken 

 into account, the results would lose much of their significance. 



To prove or disprove Liebig's ideas, Lawes, Gilbert, and Pugh, of 

 the Rothamsted Experimental Station, began in 1857 a series of 

 crucial experiments. They were so careful in handling the soil that 

 they destroyed the organism fixing the nitrogen symbiotically with 

 leguminous plants. They thus failed to become the discoverers of 

 the symbiotic fixation process. In absence of bacteria, the legume 

 behaved like cereals. This phenomenon was later confirmed by a 

 number of other investigators who showed that legumes do not 

 fix nitrogen when the soil has been ignited but do fix nitrogen in 

 unignited soil. Schulz-Lupitz grew lupines for fifteen consecutive 

 times, without application of nitrogen fertilizer and without diminish- 



