n.s7 



roniiiiUori of the Inlx'rcles. In lator stag'os of the growth of tlio 

 tubercles he Ibutid l>acteroids, but was uuable to determine whether 

 they had any connection with the hyphf© or not. 



Meantime other experimenters had been led to quite different con- 

 clusions. Binnchorst,* Tschircli,t and Van Tieghem and Doulliot| 

 concluded that the tubercles were normal products of the plants and 

 had no connection with any infection from without. The hyplia) and 

 bacteroids were always found, but were regarded as peculiar conditions 

 assumed by the protoplasm of the root cells, rather than as distinct 

 organisms. 



Results of later worlc. — IS'ew and more careful experiments within the 

 past '^ years have furnished strong indications that the tubercles are 

 not normal products, but are produced in the roots as a result of infec- 

 tion from without. Hellreigel§ found, as the result of a long series of 

 experiments, that when pea [dants were grown in sterilized soils, as a 

 rule no tubercles were formed ; but when the plants were watered with 

 soil infusions, made by allowing water to act upon soil in which peas 

 had been grown, the tubercles appeared in abundance. If the soil 

 infusion was sterilized by boiling before it was put upon the plants no 

 tubercles apjieared. These experiments were thought to prove that the 

 tubercles were really caused by living organisms in the soil infusion, 

 which were killed by heat. The tubercles could, not, therefore, be 

 regarded as normal products of the roots, but were certainly infections 

 from the soil. In a series of researches, undertaken with the assistance 

 of Wilfarth,|| these results were thoroughly contirmed. Hellriegel's 

 researches were, however, undertaken chiefly to determine the relation 

 of the tubercles to the power of assimilating nitrogen, aiul did not, 

 therefore, deal to any extent with the nature of the tubercles beyond 

 proving them to be infectious. 



The observations of Hellriegel were soon confirmed by Ward, ^ who 

 also insisted on the infectious nature of the tubercles and more care- 

 fully studied their formation. He found that the hyplue described by 

 Erickson appear early in the development of the tubercles, and after 

 growing for a while give rise, by budding, to the bacteroids. The plant 

 thus concerned in the formation of the tubercle he regarded as one of 

 the low fungi whose parasitic habits had destroyed its power of pro- 

 ducing spores. 



In 1888 Beyerinck ** reached a different conclusion as to the nature 

 of this organism, lie extended the study from peas, on which most of 

 the previous work had been done, to a largo number of leguminous 



* Vorliinf. Mitt.; Bcr. d. l)Ot. Gesell., 1885. 

 t ma., 18^7. 



X Bull, (le la Soc. Lot. de France, 3.5 (1888). 



$ Taj;cl)l. d. r)9. Vcrsaniiul. dent. Natnrf. n. Aerzto in Picrlin, 183(5. 

 \ noiIa<;clicft zu d. Zeits. d. Ver. f. d. Kiibenznckcr-ludtistrie d. d. R., 1888. 

 If Pliil. Trans. Roy. Soc, London, Vol. 178, 1887. 

 ••Bot. Ztg., Bd. 4(), 188fc. 



