CORRELATION OF REACTION OF THE SOIL 161 



made acid, F. nivale, O. gramhiis, and T. gramineum may dis- 

 appear. 



2. MesanthrophiUc: those that thrive best in neutral soils, in- 

 cluding Fusariimi aurantiacum, F. avenaceum, F. herbarum, 

 Phoma betae, and Thielavia basicola. 



3. Oxyphilic: those that thrive best in acid soils, including 

 Plasmodiophora brassicae and Rhizoctonia violacea. If the soil 

 reaction reaches pH 7.5, P. brassicae is checked. Synchytrium 

 endobioticnm may also be placed within the oxyphilic group, but 

 it is actually intermediate between this group and the aestatic 

 group. 



4. Aestatic: those that possess the ability to thrive in a wide 

 range of soil reactions, including Fusarium cidmorum, F. poly- 

 morphum, Helminthosporium sativum, Ophiobolus herpotrichus, 

 and Rhizoctonia solani. 



SchafTnit and Meyer-Hermann (1930) indicate that not only is 

 the reaction changed by the addition of acid or basic materials 

 to soil but also that such changes are always accompanied by 

 changes in the physical properties of the soil. Furthermore it has 

 become a matter of common knowledge that changes in reaction 

 may not be permanent and that changed availability of minerals 

 to growing crops accompanies changes in soil reactions. 



Chupp (1928) noted that pH 7.2 to 7.4 is the upper limit at 

 which Plasmodiophora brassicae causes club root of crucifers and 

 that in the range more acid than pH 6.0 all the plants may be 

 affected. 



In black-root rot of tobacco, soil reaction and soil tempera- 

 ture are correlated factors. Doran (1929) observed that this dis- 

 ease does not develop at any temperature provided that the pH of 

 the soil is 5.6 or lower. Marked injury is apparent, however, at 

 15° C with pH 5.7; at 18° C with pH 5.7 to 5.8; at 21° C with pH 

 5.8; at 27° C with pH 5.8 to 5.9. M 30° C there was little, if any, 

 injury with pH values of 6.0 to 6.9. 



That acid soils yield a scab-free crop of potatoes, unless lime is 

 applied, is the common experience of potato growers. Studies by 

 Gillispie (1918) on the scab organism, Actinomyces cloromo genus, 

 showed that it is inhibited at pH 4.8 to 5.2, varying with the iso- 

 lates. He correlated these results with the fact that the acidity 

 of Caribou loam of Maine ranges from 4.9 to 5.5 and hence may 

 restrain the growth of the scab organism. 



