Nov. 1896.] BOTANICAL SOCIETY OF EDINBURGH l7 



He further noticed that when the phints were grown in 

 a poor soil — poor as regards nitrogen — they all came up 

 equally well at first, and made a healthy braird, but as 

 soon as the supply of nourishment contained in the seed 

 was used up, they began to grow pale and yellow, and the 

 oats died down. The peas, however, did not die down, but 

 after a period of ill-health they began to regain their green 

 colour, and thereafter their growth was rapid, and eventu- 

 ally they attained to full development. 



He found that those plants that flourished best had most 

 nodules on their roots, and those that were most backward 

 had fewest. 



This proved that vigorous growth and the development 

 of root nodules were related to each other in some way. 



To test whether the growth of the nodules was dependent 

 on the attack of micro-organisms in the soil, he grew some 

 peas and other leguminous plants in pots whose soil he had 

 previously sterilised by heating, and he found that in such 

 soils the peas succumbed just as the oats had done ; there 

 was no revival of colour and strength as before. When, to 

 such a sterilised soil, he added a little of a fertile soil, in 

 which peas grew on a few cubic centimetres of the watery 

 extract of such a soil, the peas grew as before, and pro- 

 duced nodules on their roots. When he planted his peas 

 in a sterilised soil to which nitrogenous manure was added, 

 the peas grew, but they did not produce any nodules on 

 their roots. 



What was proved then by these experiments was, that 

 leguminous plants could grow in a soil supplied with proper 

 nitrogenous nourishment just as other plants could, but 

 that they could also grow in soils containing very little 

 nitrogenous matter if well supplied with other essential 

 manurial ingredients, and that the plants contained far more 

 nitrogenous matter than was contained in the soil ; that this 

 gain of nitrogen was dependent on the growth of nodules 

 on the roots, and in proportion to their abundance ; that the 

 appearance of nodules was possible only in soils where a 

 certain organism, or certain organisms, were present, and 

 not otherwise; that the interference of these organisms 

 enabled the plant to take up free nitrogen, either by its 

 roots or by its leaves, from the air in the soil, or from the 



TRANS. BOT. SOC. EDIX. VOL. XXI. C 



