Crystals of cadmium were grown from the vapour on a quartz fibre in an argon diffusion cell designed so that the temperature,T, could be measured and the supersaturation, σ, calculated at every point. A critical σ of ∼ 0 4 for nucleation was observed below which no crystals grew and above which the density of crystals increased with σ For ≲σ2, crystals grew as whiskers and thin platelets independently of σ andT; for 2≲σ≲102the end products were thick hexagonal plates; for σ≳102andT≲250°c spike and leaf dendrites appeared and grew to large dimensions. The observed dependence of whisker growth rates on σ and whisker radius showed that growth was probably controlled by the diffusion of cadmium vapour through argon. Evidence for both tip growth and non-tip growth of whiskers is presented.