498 THE POPULAR SCIENCE MONTHLY. 



admitted that the results so far brought forward are abundantly 

 confirmatory of those obtained by Hellriegel ; and that the fact of 

 the fixation of free nitrogen in the growth of Leguminosce. under 

 the influence of microbe seeding of the soil and of the resulting 

 nodule formation on the roots may be considered as fully estab- 

 lished." 



The results obtained by the inoculation of the prepared quartz 

 sand with the microbes of a fertile soil, or of one in which lupines 

 were growing, as shown in the increased growth of the plants in 

 pots 2, 3, 10, 11, 18, and 19, when compared with those in pots 1, 9, 

 and 17, which were not inoculated, are striking ; but a comparison 

 of the plants in the inoculated pots with those in pots 4 and 12 in 

 a garden soil, and pot 20 in a "lupine soil," furnish still more 

 significant indications of the futility of purely chemical consid- 

 erations in discussing the nutritive processes of plants and their 

 relations to the soil. The peas and vetches in a rich garden soil 

 flowered and seeded, but the plants were not as large, and the 

 root-tubercles were not as numerous, as in the sterile quartz sand 

 inoculated with microbes from a fertile soil ; and the lupines made 

 a better growth in the inoculated quartz sand than in soil from a 

 lupine field. 



The biological factors concerned in the elaboration of plant 

 food seem to be quite as important as the chemical elements pro- 

 vided in the soil itself ; and a revision of the accepted theories of 

 plant growth, and the relations of soils to their processes of nu- 

 trition, is evidently needed from this standpoint. 



It should be remarked, however, that the root-tubercles pro- 

 duced by microbes are not confined to the Leguminosce,, as they 

 have, in fact, been observed in several natural orders of plants. 

 Moreover, there are indications that several varieties or species of 

 symbiont microbes are concerned in the production of tubercles 

 on the roots of leguminous plants, and it is probable that each 

 species has its own favored form. 



Hellriegel failed to grow lupines in a nitrogen-free soil inocu- 

 lated with a fertile soil-extract ; but, when the inoculation was 

 made with an extract of a sandy soil in which lupines were grow- 

 ing, a luxuriant growth was obtained. 



In the Rothamsted experiments on land where red clover had 

 been grown repeatedly, and its yield of nitrogen was reduced to 

 but 22 pounds per acre, vetches, on an average for three years, 

 obtained 120 pounds of nitrogen per acre ; lucern yielded as 

 high as 340 pounds, and made an average for six years of 150 

 pounds of nitrogen per acre ; and Bokhara clover yielded crops of 

 130 and 145 pounds of nitrogen per acre. On land where beans 

 had been grown almost continuously for thirty-two years, and had 

 '' practically failed " to grow, their yield of nitrogen per acre hav- 



