Alleles of the B and R loci collec:ed from different geographic races of maize differ with respect to concentration, pattern, and tissue specificity of anthocyanin formation. No differences were found between the pigments formed by B action and those formed by R action. The activities of four B alleles and five R alleles when compared in a common genetic background and described in terms of the whole life cycle show differences in the following respects: In a given tissue, for example the aleurone, there are differences in a ) rate of activity, b) time of onset of activtiy, c) time that activity ceases. Apparent tissue specificity is shown when the development of a tissue coincides with the period during which the gene is active. True tissue specificity is shown by alleles that have different activities in tissues that develop at the same time. This latter type of specificity was shown only by alleles known to consist of more than one synaptically homologous region, or by those derived in some way from such complex alleles. It is suggested that for most genetic systems there probably exists potential for change in level of action, change in time of onset and termination of activity, and change toward tissue specificity. The type and extent of the change tolerated will depend on the system involved.

Two classes of flavonoid pigments commonly found in Zea mays are anthocyanins, which can be produced in almost any tissue, and phlobaphenes, which are found predominantly in the cob and pericarp. Chromatographic analysis of genetic stocks shows that the R locus controls the production of anthocyanins and other flavonoids hydroxylated at the 3-position, together with their precursors, and the P locus controls the production of C-glycosylflavones and their precursors; the 3-deoxyanthocyanins, and the phlobaphenes. The two pathways are controlled independently, even though there are some precursors common to both pathways. A scheme for the genetic control of flavonoid synthesis in maize is presented, and possible mechanisms for the independent control of the two pathways are discussed.

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Electron-microscope studies indicate that the aleurone tissue of maize (Zea mays L.) starts developing approximately 10-15 days after pollination in stocks that take ca. 40 days for the aleurone to mature completely. Development commences when specialized endosperm cells adjacent to the maternal nucellar layer start to differentiate. Differentiation is characterized by the formation of aleurone protein bodies and spherosomes. The protein bodies of the aleurone layer have a vacuolar origin whereas the protein bodies of the immediate underlying endosperm cells appear to develop from protrusions of the rough endoplasmic reticulum. Thus, two morphologically and developmentally distinct types of protein bodies are present in these adjacent tissues. The spherosomes of the aleurone layer form early in the development of this tissue and increase in number as the tissue matures. During the final stages of maturation, these spherosomes become closely apposed to the aleurone grains and the plasma membrane. No further changes are apparent in the structure of the aleurone cells after 40 days from pollination when the caryopsis begins to desiccate.