- 1 The distribution of spawn ponds of the frog in an area with a varied geology is not at random. The frogs avoid London Clay ponds.
- 2 Significant relationships have been found between the potassium content of the water of ponds and the presence or absence of spawn. Carbonates also affect the spawn distribution.
- 3 There is some evidence that concrete ponds or concrete structures in streams favourably affect the chances that frogs will spawn at such places.
- 4 Pollution by sewage seems a favourable factor.
- 5 The mechanism by which such factors can act is discussed, and it is suggested that indirect action is most likely, through the intermediary of the micro-flora.