Fig. 5.

Representative whole‐fruit histological sections 6 and 8 d after pollination (DAP) from intra‐ and interspecific crosses among Mimulus caespitosa (C), Mimulus tilingii (T), and Mimulus guttatus (G). Maternal parent is listed along the left side, and paternal parent is listed along the top. Along the diagonal are the intraspecific crosses (C×C, T×T, and G×G), below the diagonal are maternal‐excess crosses (T×C, G×T, and G×C; maternal parent always listed first), and above the diagonal are paternal‐excess crosses (C×T, T×G, and C×G). Arrowhead, embryo; en, endosperm; sc, seed coat. Bars, 0.1 mm. (a) Six days after pollination. Intraspecific and paternal‐excess endosperms are mostly composed of large empty cells, whereas maternal‐excess crosses (especially G×T and G×C) develop endosperms that are small and composed of darkly stained, dense cells. (b) Eight days after pollination. Intraspecific endosperm cells begin to differentiate into cytoplasmically dense, starch‐filled cells along the peripheral region near the seed coat. However, in G×T and G×C crosses, the whole endosperm is composed of these dense cell types, and the endosperm remains very small and compact. Paternal‐excess endosperms appear abnormal and do not show evidence of dense cell types by 8 DAP.