434 Transactions. — Botany. 



the other thirty vessels in which the introduction of micro- 

 organisms was left to chance, only two at this stage pre- 

 sented a similar appearance, all the rest were still starving 

 and in part yellow. A fortnight later the plants in the 

 ten vessels were developing their tenth leaf and growing 

 luxuriantly. Of the sixty plants in the other culture-vessels 

 which had not been supplied with bacteroids ten were now 

 nearly as flourishing as the above, while five were nearly 

 dead. Among the remaining forty-five plants all stages 

 between these extremes were to be found. An examination 

 of the roots of the best grown and the worst grown plants 

 fully confirmed the relation between the growth of the sub- 

 aerial parts and the development of root-tubercles. This 

 experiment did not, however, furnish a decisive answer to 

 the question of the source of infection of the roots with the 

 organisms that produce the tubercles. Abundant tubercles 

 had appeared on plants grown in culture-vessels to which no 

 soil-washings had been deliberately added, the micro-organ- 

 isms having been introduced in some unknown and accidental 

 way. 



The question was attacked anew, and this time with more 

 decisive results. Two cultivations were made in soil free 

 from nitrogen, to which the usual non-nitrogenous nutritive 

 mixture, and, in addition, a small amount of the above- 

 mentioned soil-washings, were added. The culture vessels 

 thus charged were then sterilised by heating, after which 

 the seeds were sown and the surface of the soil covered 

 over with sterilised wadding. All went well until the de- 

 velopment of the sixth leaf and the setting in of the usual 

 starvation stage. After this the plants made no further 

 progress, and before long all of them died. No tubercles 

 were formed on the roots under these circumstances, and 

 numerous repetitions of the experiment always gave the 

 same results. These experiments show conclusively that 

 the formation of the root - tubercles is dependent on the 

 presence of living micro-organisms in the soil, which infect 

 the roots, and that in the absence of root - tubercles legu- 

 minous plants are exactly in the same case as other plants 

 — they pass into a condition of permanent starvation as soon 

 as the food reserves of the seed are exhausted, just as 

 gramineous plants do when grown in a medium devoid of 

 available nitrogenous compounds. 



Hellriegel sums up the outcome of his researches in these 

 terms : " Leguminous plants, in contrast to the gramineous 

 ones, are not dependent on the soil for their nitrogenous 

 nutrition." As to the source of their supplies of nitrogen, he 

 adds, " Not one of my experiments supports the idea that it is 

 to be found in the minute quantities of combined nitrogen 



