Io82 SOIL PHYSICS, CHEMISTRY AND MICROBIOLOGY 



able to promote the growth of an azotobacterial flora. If calcium sulphate is 

 then added to the solution, all the soils do not behave in the same way; in 

 some a regular growth of the Azotohacter is observed, and no growth of the 

 others. These differences in behaviour are taken to be due to the percent- 

 age of alkaline carbonates, which varies from soil to soil. This furnishes 

 the elements for a new biological method of determining the content of 

 the soil in basic substance (i). 



IV. — Enquiries into the Relation between the Composition of the Soil 

 and the Presence of Plasmodiophora brassicae. — Applying the microbio- 

 logical method for determination of the soil reaction, the Writer was able 

 to demonstrate the existence of a fairly close relation between the presence 

 of Plasmodiophora brassicae and the alkalinity of the soil. The greater the 

 the reduction in the latter, the greater the likelihood of attack, which is 

 almost impossible in a markedly alkaline medium. I. Kolpin Ravn also 

 studied the relation between the behaviour of the soil and the presence of 

 various grass plants, arriving at the conclusion that the terms calcifugal 

 and calciphilous plants ought to be replaced by the terms basifugal and basi- 

 philous plants, or acidifugal and acidiphilous. Acidiphilous species would 

 be : Rumex acetosella, Raphanus raphani strum, Viola tricolor, Scleranthus 

 (?) annuus, Cynaphalium uliginosum, Spergula arvensis ; and basiphilous 

 species, Sinapis arvensis and Veronica agrestis (2). 



V. — On the Fixation of atmospheric Nitrogen by free Microorganisms. 

 — A comprehensive study of the most important researches in connection 

 with this question, and the results obtained by the Writer's experi- 

 ments (3). 



VI. — • In connection with the decomposition of Urea. — A preliminary 

 note to a study of the action of humus compoimds on the splitting up of 

 urea into ammonia (4). 



VII. — Investigations in reference to determining the Lime Requirements 

 of the Soil (5). 



VIII. — Influence of Humus on the Ammonification of Urea. — The gen- 

 erally adopted opinion that humic substance cannot supply organisms with 

 carbon as a food is incorrect. It results from these investigations that, in 

 reality, many microbes capable of splitting up urea can not only utilise the 

 humic substance, but even prefer it to all the other compounds of carbon ex- 

 perimented with (laevulose, xylose and various organic acids). There are 

 also organisms which possess the property of decomposing urea even in the 

 absence of any other organic substance, utilising it as a nutrient medium ; 



(i) Tidsskrift /or Landbrugets Planfcavl, Vol. XIV, pp. 292-294. Copenhagen, 1907. — Cen- 

 (ralblatt fiir Bakteriologie, Parasitcnkundc und Infcktionskranhheiien 11, Vol. XIX, pp. 735-736. 

 Jena, 1907. 



(2) With Kolpin-Ravn 1'. and Harder P. Tidsskrift for Landbrugets PlatUeaii, \'ol. XVI, 

 pp. 430-476. Copenhagen, 1909. 



(3) Tidsskrift for Landbrugets Planteavl, Vol. XVI, pp. 303-336. Copenhagen 1009. 



(4) Centralblatt fiir Bakteriologie, Parasitenkunde und Infektionskrankhfiten IT, Vol. XXIV, 

 ji. 130. Jena 1909. 



(5) WithLarsen O. ri. ;scc/iH//c/mfor Jamuu y 1911, No. 59. (Ed.) 



