OVULE DEVELOPMENT IN ORNITHOGALUM CAUDATUM (LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION

Abstract

SUMMARY Ornithogalum ovules are bitegmic: the inner is initiated first, but both attain maturity at the same time. Both integuments are derived from the epidermal layer of the nucellus and are covered by a cuticle. Inner integument cells define the micropyle and those which line it are secretory. An outer integument is present only on the distal (non‐funicular) side of the ovule. Its proximal portion apparently is fused congenitally with the funiculus. A funiculus attaches the ovule (and seed) to placental tissue. Proliferation of cells at the base of the funiculus contributes to development of the obturator. Funicular curvature causes the ovules to assume an anatropous orientation. A procambial strand branches from a ventral vein of the carpels and differentiates acropetally in the funiculus. At ovule maturity, vascular tissue terminates in the chalaza a few cells removed from the hypostase. Terminal cells of the vascular bundle consist only of tracheary elements with annular thickenings.

OVULE DEVELOPMENT IN ORNITHOGALUM CAUDATUM (LILIACEAE) WITH A REVIEW OF SELECTED PAPERS ON ANGIOSPERM REPRODUCTION

“…We have speculated concerning the function of certain phenomena seen in a developing megagametophyte and, as stated in our first paper (Tilton and Lersten, 1981), we have viewed these with respect to the whole ovule which we regard as a biological unit.…”

“…Tissues from gynoecia ranging in age from the third fioral plastochron through receptive fiowers were studied. Because the methods used are detailed in the first paper of this series (Tilton and Lersten, 1981), they are only summarized here. Tissues were processed in glutaraldhyde and OSO4 buffered with sodium cacodylate, triple-fixed with unbuflFered uranyl acetate, and embedded in Luft's epon (Luft, 1961).…”

“…In summary, this paper has dealt with development of the megagametophyte in Ornithogalum in some detail, and we have given perspective to our observations by a rather comprehensive comparison with existing literature which seems relevant. We have speculated concerning the function of certain phenomena seen in a developing megagametophyte and, as stated in our first paper (Tilton and Lersten, 1981), we have viewed these with respect to the whole ovule which we regard as a biological unit.…”

“…2) and polarizing optics indicates that they probably are lignified. Secretory activity ofthe nucellar cap and inner integument cells which line the micropyle fills the micropyle with an exudate before anthesis (Tilton, 1980a;Tilton and Lersten, 1981).…”

“…At one extreme, the entire nucellus may degenerate and be completely absorbed. This condition is best exemplified in ovules which form integumentary tapeta, such as Helianthus (Newcomb,\91'i2i,h), Jasione (Campanulaceae) (Erdelska, 1975), Bellis (Engell and Peterson, 1977), Nicotiana (Mogensen and Suthar, 1979), and Saintpaulia (Gesneriaceae) (Mogensen, 1981) among many others (Tilton and Lersten, 1981). In Proboscidea (Martiniaceae) (Mogensen, 1978b) the entire nucellus degenerates and is absorbed, but an integumentary tapetum does not form.…”