SUMMARYOf various inorganic ions tested for their ability to stimulate hatching of eggs of the cyst nematodes of cereals (Heterodera avenae Woll), carrot (H. carotae Jones), cabbage (H. cruciferae Franklin), soybean (H. glycines Ichinohe), pea (H. goettingiana Liebs.), potato (H. rostochiensis Woll.), beet (H. schachtii Schm.), tobacco (H. tabacum Lownsbery & Lownsbery) and clover (H. trifolii Goffart), some were active. Zn2+ hatched many eggs of seven species and some of H. goettingiana, but inhibited hatch of H. avenae to below that in water. Zinc salts are the first recorded very active hatching stimulants for H. glycines in vitro. Many other metal ions stimulated hatching of H. schachtii eggs to varying extents; these also hatched some but not all of the other species. Vanadate ions were particularly effective for H. rostochiensis, more so than Zn2+. No ion increased the hatch of H. avenae to above that in water. The most active ions were not those most abundant in soil.The behaviour of different ions with different species did not suggest any obvious affinities between species, but the differences between the hatching of H. tabacum and H. rostochiensis add weight to the view that, despite morphological similarities and overlapping host ranges, they are distinct species rather than pathotypes of a single species.Ions and other hatching agents may be absorbed by materials within the egg or larva and alter the structure and function of these materials. The lack of correlation between the hatching of H. schachtii by ions and the known stability sequences of various biological metal‐binding systems suggests that there may be several sites of action that differ in their response.

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SUMMARYOf 444 compounds tested for their ability to stimulate eggs of Heterodera rostochiensis to hatch, forty‐five did so to varying extents. Many compounds that hatched H. schachtii Schm. eggs did not hatch H. rostochiensis eggs. The most effective compounds with H. rostochiensis were picrolonic acid, anhydro‐tetronic acid and vanadates. Tests with analogues of picrolonic and anhydro‐tetronic acids suggested some structures that may be concerned in hatching H. rostochiensis and H. schachtii. The simple analogues hatched the eggs of H. schachtii but not those of H. rostochiensis. Suitably placed polarisable atoms seemed to be an essential feature. Picrolonic acid contains pairs of polarizable atoms, about 4 and 6·7 Å apart, that may respectively be associated with the hatching of H. schachtii and H. rostochiensis. Other features of the more active hatching agents were a cis and co‐planar arrangement of the two polarizable atoms with respect to the rest of the molecule. The function of hatching agents is discussed.

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