Evidence is produced to indicate that the major alkaloids of hemlock, coniine and γ-coniceine, occur as bound forms as well as the normal free salts. These bound forms vary from ethanol-soluble substances which readily break down into coniine or γ-coniceine, to larger, more resistant, water-soluble complexes which on vigorous treatment break down to alkaloid-like compounds. The quantities vary during fruit development and it is suggested that the alkaloids are built up into a series of compounds of increasing complexity which may play an important part in the metabolism of the fruit.