Botanical Review 13(8): 423-477 (Oct 1947)
The Endosperm in Seed Development
R. A. Brink and D. C. Cooper

pp . 455-456

IRIDACEAE

The cross Iris pseudacorus x I. versicolor yields shrunken seeds which do not germinate. Sawyer (215) found that selfed seeds appeared to form a few more nuclei in the free-nucleate endosperm than hybrid seeds before 13 days, at which time wall formation was initiated in both cases. Endosperm food reserves were much more abundant in the normal seed than in the hybrid at 20 days. The cells of the hybrid endosperm were almost without contents at 26 days; and at six weeks the tissue had collapsed, forming a dark-colored jacket around the embryo. The endosperm in the normal seed persists to maturity.

Lowig (150) observed that fruits formed after the cross I. sibirica ♀ x I. pseudacorus ♂ but were significantly smaller than the normal. The ripe capsules contained numerous shrivelled and non-germinable seeds which Lowig believed were without endosperm and embryo. Two possible explanations were suggested to account for these abortive seed-like structures: (a) fertilization had occurred but endosperm and embryo had failed of development, or (b) the empty seeds were the result of a pollination stimulus like that which Fitting (76) had established in the orchid. The reciprocal cross, I. pseudacorus ♀ x I. sibirica, ♂ gave fewer but larger seeds containing identifiable embryos. Lowig was unsuccessful in germinating them.

Crosses between different groups of cultivated irises, according to Werckmeister (272), rarely form normal seeds. Instead of firm endosperm tissue, a pulpy mass develops which becomes brown and hard on drying. Embryos are frequently present but are variously developed. Werckmeister, on observing that sound embryos dissected from mature seeds and placed on a nutrient medium swelled very rapidly and often died, attributed a dual role to the endosperm. He believed the tissue provided a nutrient reserve and regulated the absorption of water by the embryo. The seed failure attending Iris crosses was mainly due, in Werckmeister's judgment, to lack of development of an endosperm which would function effectively at germination in controlling the rate of water uptake.

Botanical Review 13(9): 479-541 (Nov 1947)
The Endosperm in Seed Development (Concluded)
R. A. Brink and D. C. Cooper

pp. 526-527

Tukey (256), working with early varieties of the sweet cherry, found that embryos enclosed in the endosperm, nucellus and integuments did not grow in culture unless the swelling of the embryo was sufficient to burst the integuments and expose the cotyledons to light. Normally developed Iris seed, when sown in the soil, germinates over a period of three years (272). By artificial cultivation of excised embryos, seedlings were obtained in a few days. A procedure was also worked out whereby about 95% of the embryos excised from mature Iris seeds, and grown in a nutrient medium, yielded seedlings (204). Granular sodium hexametaphosphate (Calgon) was used as a source of phosphorus in a 0.7% agar medium containing 2.0% cane sugar, together with other mineral salts. The hexametaphosphate forms a soluble complex with both iron and calcium. Embryos completely detached from the endosperm germinated promptly in the medium. Growth was inhibited, however, if even a small portion of endosperm tissue remained in contact with the embryo. Randolph (203) has recently described an improved method of cultivating embryos excised from Iris seeds showing delayed germination. McLean (153) notes that Datura ceratocaula seeds ordinarily give about 0.1% germination. Practically complete germination was secured, however, by cultivation of the excised mature embryos in a nutrient medium.

Hetero-Fertilization / Endosperm Failure