In 1924, Morgan visited South Lincolnshire to investigate the part played by the potato-root eelworm (Heterodera schachtii) in the serious failure of the local potato crop: a note on the investigation appears in this Journal (1925, p. 185). A second visit was made in 1925, as a result of which certain conclusions regarding manuring and the rotation of crops were put forward (this Journal, 1926, p. 49). Towards the end of 1925 the second writer (Peters) made a hurried survey with the object of seeking a possible correlation between the distribution of eelworm cysts and the hydrogen ion concentration of the soil. Such a correlation was actually demonstrated (this Journal, 1926, p. 87) in the case of a selected field for which Morgan had complete data of cyst-counts. The question thus arose as to whether any clear correlations should be shown to exist between the three factors: concentration of cysts, pathological condition of the crop, and reaction of the soil. In other words, was the eelworm associated with the damage? and was it controlled (and therefore controllable) by the effective acidity of the soil? To decide these questions might be a matter of considerable importance, particularly if the eelworm was found to be responsible for the damage, for affirmative answers would open the way to effective treatment, by the adequate liming of soils for instance.