Pot experiments in glass-house and garden were used to investigate early growth check in naturally occurring and directly sown seedlings of Scots pine (Pinus sylvestris ssp. scotica) on many Scottish peats. The peats used are described and compared for their content of K, Ca, Mg, P, N on a dry weight and volumetric basis. The occurrence of growth check and mycorrhizal root infections among the experimental seedlings is noted and analysis of their shoots compared with that of the peaks. Only P and N were found to be in such short supply that seedling growth was limited and deficiency symptoms produced, and then only in seedlings lacking mycorrhizal rootlets. It is concluded that, under certain conditions important in natural seedling establishment, absence of mycorrhiza can be a direct cause, and not merely a result, of early growth check.