1 8 TRANSACTIONS AND PEOCEEDINGS OF THE [Sess. Lxr. 



air above the soil, in some unknown manner ; that in the 

 nodules there was a supply of nitrogenous matter which 

 disappeared as the plant grew older, and that some of the 

 nitrogenous matter of the nodules, and the organisms along 

 with it, found their way back to the soil, and caused it to 

 become richer in nitrogenous compounds. 



This beautiful, interesting, and important discovery was, as 

 I have said, first communicated by Professor Hellriegel and 

 his coadjutor, Dr. AVilfarth, but there were a good many 

 others engaged in the same inquiry, and whose experiments 

 led to similar conclusions. Chief among these were Professor 

 Prazmouski, Berthellot, Attwater, and Marshall Ward. 

 The last of whom has shown, in a paper read before the 

 Eoyal Society of London (1887), that the organism which 

 attacks the roots of the leguminos;e, causing the gi'owth of 

 nodules, is not a bacterium, but a fungus whose minute 

 germs are all but universally distributed in the soil. 



The much debated question is now solved. The loss 

 which is constantly going on over the world in the con- 

 version of combined into free nitrogen is being constantly 

 recouped by the conversion of free atmospheric nitrogen 

 into combined nitrogen by at least one sub-order of plants 

 that is found abundantly distributed all over the world. 



The question naturally arises, are the leguminous the only 

 kind of plants possessing this faculty of nitrogen assimila- 

 tion ? It would add vastly to the wonder of the process if 

 that were so, and it would invest this sub-order of plants with 

 a fascinating and absorbing interest. It is not natural to 

 suppose that this power should be limited to only one 

 sub-order of plants, and it would seem that other orders 

 of plants are now recognised as in active, though it may be 

 feeble competition. There is, however, one important set 

 of plants that has been found to possess the faculty in a 

 marked degree, viz. unicellular alga:', whicli, though among 

 the most minute of plants, make up by their number what 

 they lack in size. This very important discovery was made 

 by Berthellot and Andre. They found that soils in which no 

 visible plants were growing, and from which all combined 

 atmospheric nitrogen was excluded, did become richer in 

 nitrogen, whose only source can be the free nitrogen of the 

 air ; and a microscopic examination of such soils shows the 



