PMC

Developing fruits resulting from Mimulus guttatus and M. nudatus self-fertilizations and reciprocal crosses of M. guttatus × M. nudatus, as well as images of mature seed recovered from self-fertilized and hybrid fruits. All crosses are female × male. (a) M. guttatus self-fertilized fruit. (b) M. nudatus self-fertilized fruit. (c) M. guttatus × M. nudatus fruit. (d) M. nudatus × M. guttatus. (e) Round M. guttatus seed; shriveled and flat M. guttatus × M. nudatus seed. (f) Round M. nudatus seed; shriveled and flat M. nudatus × M. guttatus seed. All seed types appear to have developed a seed coat.

Comparison of self-fertilized Mimulus guttatus and M. nudatus seed at 5 d after pollination (DAP) (a–d) and 9 DAP (e–i). Reciprocal M. guttatus × M. nudatus hybrid seed exhibit delayed embryo growth and impaired endosperm development. All crosses are female × male. en, endosperm; em, embryo: mh, micropylar haustorium; mn, micropylar nuclei; sc, seed coat. (a) M. guttatus self-fertilized seed at 5 DAP. Endosperm is densely packed and embryo is at the globular stage. (b) M. guttatus × M. nudatus seed at 5 DAP. Endosperm resembles that of self-fertilized M. guttatus, but embryo is delayed at 8-cell stage. (c) M. nudatus self-fertilized seed at 5 DAP. Endosperm is densely packed and embryo is at the 16-cell stage; micropylar nuclei are also visible. (d) M. nudatus × M. guttatus seed at 5 DAP. Endosperm is poorly developed and embryo is at the 8-cell stage. (e) M. guttatus seed at 9 DAP. These seeds have a well-developed seed coat, densely packed endosperm, and a torpedo stage embryo. (f, g) M. guttatus × M. nudatus seed at 9 DAP, with loosely packed and irregularly deposited endosperm and a heart stage embryo. (h) M. nudatus seed at 9 DAP with densely packed endosperm and a heart stage endosperm. (i) M. nudatus × M. guttatus seed with irregularly developed endosperm and late globular stage embryo.

Images of pollen tubes penetrating the ovaries within 24-h of pollination for interspecific crosses of Mimulus guttatus and M. nudatus. Pollen tubes are stained with aniline blue and visualized with a Zeiss Axio Observer equipped with a fluorescent lamp and DAPI filter. (a) An unpollinated M. guttatus ovary. (b) Pollen tubes from M. nudatus pollen growing down a M. guttatus style. (c) Pollen tubes from M. guttatus pollen growing down a M. nudatus style.

Growth trajectories of self-fertilized and hybrid seed, pooled across accessions. Points represent the mean ± SD. All crosses are female × male. For seed size increase by accession, see . (a) Mimulus guttatus self-fertilized seed and M. guttatus × M. nudatus hybrid seed. (b) M. nudatus self-fertilized seed and M. nudatus × M. guttatus seed. DAP, days after pollination.