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The genetic control of isozymes from Citrus and its near relatives was determined for three gene/enzyme systems: glutamate oxaloacetate transaminase, phosphoglucose isomerase and phosphoglucose mutase. These enzymes are controlled by four genes having 19 codominant alleles, 12 of which occur in Citrus subg Citrus. Formal genetic studies were carried out with F, biotypes and F1 populations of known origin. When biotypes were grouped into traditionally recognized species to examine genetic affinities within and between species, a remarkable pattern of uniformity of genotype combinations was found within a species, and every species had an unique combination. Because many economically important cultivars produce asexual(nucellar) as well as sexual(zygotic) embryos, a central problem of the breeder is to distinguish these when plants are young, long before fruiting. Isozyme markers can be used with varying degrees of efficiency, depending on the genotypes of the particular parents, to distinguish nucellar seedlings from those of zygotic origin.

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The legend for figure 10 on page 373 does not agree with the orientation of the photograph. To read correctly, the photo should be turned 90 degrees clockwise with the rule at the bottom.Hybrids of 'Eureka' and 'Lisbon' lemons were studied along with their parents and possible ancestral types to investigate the phylogeny of Citrus Zintort (L.) Burm. f. Data on leaf, flower, and fruit characters were collected and analyzed for inheritance of specific characters and for the amount of variability. Leaf and rind-oil components were analyzed by gas chromatography. Those hybrids producing suscient microspores were studied for meiotic abnormalities. Segregation of all characters studied demonstrates the heterozygosity of C. limo*. Color (anthocyanin) development in flower buds and young leaves is most likely controlled by a single dominant gene. Color on the young stems may be controlled by two dominant genes, one of which also controls color in flower buds and young leaves. Preformed root initials are most likely controlled by one, and leaf articulation by at least two genes.Characters specific to C. medica were present in the lemon progeny, indicating definite involvement of the citron in the lemon ancestry. Some characters indicate a possible common gene source with C. amadfolk and C. jambhiri. The deviation of some hybrids from their parents or proposed ancestors indicates a contributing gene source that has not yet been identified.The presence of much sterility and wide segregation of characters argues against the specific standing of C. & m m . It has a common gene source with the citron-lime group, and it may be a derived hybrid involving some unidentified taxa. The overlapping geographical distribution of various Citrus taxa at the assumed place of origin of C. 1imo.n further suggests the possibility of intercrowing or common origin of various Citrus species.

A B S T RAe T Comparative cytological and histological studies during embryogenesis of seeds from 2x X 2x and 2x X 4x crosses indicate that the ratio of ploidy level between embryo and endosperm is the most important factor affecting the course of seed development. The crosses produced seeds with the expected ploidy relationships between embryo, endosperm, and maternal tissue of 2:3:2 and 3:4:2 as well as the anomalous relationships 3:5:2, 4:6:2, and 6:10:2. All but 3:4:2 resulted in normal, germinable seeds. The ploidy level of the maternal tissue in relation to that of the embryo or endosperm did not appear to have any effect on seed development. About 92-99 % of seeds from 2x X 4x crosses containing triploid embryos with tetraploid endosperm aborted at different stages of embryogenesis. The abortion in all cases was preceded by abnormalities in the tetraploid endosperm. It is postulated that the unbalance of chromosome number between embryo and endosperm disturbs physiological relationships between these two tissues, leading first to the abortion of the endosperm and then of the embryo.

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