■'20 



SCIENCE. 



LN. S. Vol. XVII. No. 418. 



,Chese plants. The hearty applause with 

 which this announcement was received at 

 ■ the meeting, and the widespread and spon- 

 taneous interest which it awakened all over 

 the world, showed that it came as a relief 



'' jto agricultural chemists and vegetable 

 jphysiologists in general. The report of 

 |i€llriegel was based upon observations 

 ;and experiments made during the four 

 preceding years. He had been appointed 



' jointly with Wilfarth as referee on the 

 ^'ubject of nitrogen assimilation by plants. 



» The experiments were made in pots con- 

 taining four kilos of recently ignited sand, 



•• 'to which the proper, amount of mineral 

 j)lant food, free from combined nitrogen, 

 ha^ been added. The main points estab- 



•" lished were as follows: 



1. "When no combined nitrogen was 

 added to the artificial soil the acquisition 

 of nitrogen over that contained in the 



•' seeds was naught. This was true for all 

 ■' kinds of plants, including the legumes. 



2. The development of all kinds of plants 

 and the acquisition of nitrogen were in 

 direct proportion to the amount of com- 

 ,bined nitrogen added. 



, 3. When a small quantity of natural soil, 

 or of an aqueous infusion of such soil, was 

 added to the contents of the pots and no 

 other combined nitrogen introduced, the 

 graminaceous plants, as well as some other 

 families of plants, died of nitrogen starva- 

 tion and their acquisition of nitrogen was 

 naught. 



4. Under the same conditions the legu- 

 minous plants, after a period of nitrogen 

 starvation, began to recuperate, the foliage 



i returned to its normal green color, and the 

 plants continued to grow, in some cases 

 vigorously, to complete maturity, and ac- 

 quired all the nitrogen necessary for this 

 development. 



5. The graminaceous plants are depend- 

 ent upon the combined nitrogen of the soil 

 for their development. 



6. The legumes are independent of the 

 combined nitrogen of the soil and can ac- 

 quire all the nitrogen for their complete 

 development from the air, and, further- 

 more, not from the small quantity of com- 

 bined nitrogen contained in the air, but 

 from the free nitrogen. 



7. Whenever, under these conditions, the 

 legumes acquired nitrogen, this acquisition 

 was invariably accompanied with the ap- 

 pearance of tubercles on their roots. 



8. Sterilization of the natural soil or of 

 the soil infusion destroys its effect. 



A year later, 1887, Wilfarth made a 

 further report on this subject. In one 

 experiment made by Hellriegel and Wil- 

 farth the classical method of Boussingault 

 was employed. They placed into a large 

 glass globe four kilos of ignited sand, 

 mixed with sufficient water and the neces- 

 sary mineral constituents of plant food 

 free from nitrogen compounds. They also 

 added a small quantity, an aqueous in- 

 fusion, of a soil in which peas had been 

 previously grown. In the artificial soil 

 thus prepared they planted a pea, a grain 

 of oats and a buckwheat seed. The globe 

 was hermetically sealed with a ground- 

 glass stopper, and the necessary carbon 

 dioxide for the growth of the plants was 

 introduced from time to time. The oat 

 and buckwheat plants grew only till the 

 seeds had become exhausted, and acquired 

 no nitrogen in -excess of that contained in 

 the seeds. On the other hand, the pea 

 plant made a vigorous and normal growth 

 and was still growing, when the report was 

 made. A large part of this plant had been 

 removed and was found to contain 6.55 

 grams of dry matter and 0.137 gram of 

 nitrogen. 



This interesting experiment not only cor- 

 roborates the claims of these investigators, 

 but it completes the original experiment 

 of Boussingault, in that it restores the con- 

 dition of natural soils, which he had de- 



