There have been few studies of the metabolism of germinating seeds during the first minutes and hours of imbibition. This is partly because most biochemical techniques are unsuitable for studying these biological systems. One technique that has been developed for studying such systems involves using tritiated water as a tracer. In this technique the biological material is placed in tritiated water for a known time and then extracted. The extracts are chromatographed on paper and the tritium labelled compounds are detected by scintillation radioautography. The technique has already been successfully applied to the study of intact seeds of two species of dicotyledons. In this present work the technique was used to study the metabolic development during the first six hours of imbibition of the different parts of seeds from four species: a monocotyledon (barley), two dicotyledons (Phaseolus vulgaris and castor oil), and a gymnosperm (Pinus radiata). The seeds of these species are representative of the majority of seeds in the plant world. The results show that performing experiments on excised parts of seeds provides additional information to that obtained from using intact seeds. The most important conclusion of this work is that the axes and embryos of all seeds develop the same basic metabolic pathways during the first hours of imbibition and that these pathways develop in a similar order. Amino acid metabolism begins during the first few minutes of imbibition, followed by the metabolism of Krebs cycle acids and, after two hours, sucrose metabolism. Ten different labelled compounds were identified and labelled groups of compounds described as lipids and sugar phosphates were also present. Detailed conclusions are made about the metabolism based on the tritium labelled compounds formed, together with any other relevant information available. A number of additional experiments, including ¹⁴C tracer experiments, were performed on parts of two of the seeds. These experiments enabled more definite conclusions to be made about the metabolism of sucrose and 4-aminobutyrate, two of the compounds labelled in the tritiated water experiments. Most and in some cases all the labelled compounds formed in the axes and embryos were also found in the storage organs. However, the rate of metabolic development of the storage organs was slower than that of their corresponding axes or embryos, and a comparison of water absorption to metabolism indicated that initially this may have been due to their slower water absorption. The metabolic development was not as uniform among the storage organs as it was among the embryos and axes. In particular, the barley endosperm appeared to have a much simpler metabolism than the castor oil endosperm and it was shown that its metabolism occurred entirely in the aleurone layer of cells on its surface. It is concluded that the metabolic development of seed storage organs depends more on their morphology and function than on their embryological origin.