90 MASSACHUSETTS HORTICULTURAL SOCIETY. 



the legumes, that is to saj', peas, seradella, and lupines, after 

 having consumed the reserve material of the seed and then fasted 

 for a time, suddenly began to turn dark green, and from that 

 moment grew luxuriantly until they ripened. But if the soil 

 solution had been sterilized before it was applied it remained 

 without effect. The different soils used did not all work in the 

 same wa}'. With lupines and seradella, only soil in which these 

 plants had been grown manifested this behavior ; with peas, on 

 the other hand, all the cultivated soils were effective. The expe- 

 riments were made in a large number of pots — one hundred and 

 seventy-eight all toid. As was clear from photographs of the 

 plants, they gave results which agreed so well with one another 

 that accidental presence of nitrogen in the sand or other errors 

 were excluded. It is thus to be considered as proven that the 

 legumes are able to get their nitrogen entirely from the air. Our 

 experiments of the past year make it very probable that peas were 

 able, not onh' to take up the small quantities of combined nitro- 

 gen, but also to assimilate the free nitrogen of the air. And the 

 experiments of this year demonstrate this still more conclu- 

 sively." 



One of Professor Hellriegel's experiments is particularly inter- 

 esting. It was made upon the plan of experiments by Boussin- 

 gault, which have long been taken as part of the evidence that 

 plants cannot obtain nitrogen from the air. The plants were 

 grown inside large glass globes, through which air, free from 

 nitrogen, was passed ; the mineral food of the plants was supplied 

 in the soil in which they grew, and carbonic acid was introduced, 

 so that they had everything ordinarily supposed to be necessary 

 for their growth except nitrogen. That is, they had the free 

 nitrogen of the air, but in no other form except the minute quantity 

 contained in the soil infusion which was added. This soil infusion, 

 which, according to Hellriegel, contains the micro-organisms that 

 help the plants to get hold of the free nitrogen, made the diflfer- 

 erence between his experiments and those of Boussingault. None 

 of Boussingault's plants obtained any considerable quantity of 

 nitrogen. 



Hellriegel's plants were peas, buckwheat, and oats. The two 

 latter acquired no oxygen and, of course, made extremely' little 

 growth ; but the peas grew luxuriantly and were entirely normal. 

 I ought to add that, in his last paper Professor Hellriegel speaks 



