Ovular Development and Morphology of the Outer Integument of Magnolia grandiflora (Magnoliaceae)

Abstract

Ovular development of Magnolia grandiflora was examined to determine the morphology of the outer integument. At the time the ovular primordium begins incurving, the outer integument is initiated subdermally, and later the inner integument arises from the dermal layer. Whereas the inner integument is annular, the outer integument is formed as a semiannular rim interrupted on the concave side of the funiculus. Later the outer integument becomes a hood-shaped envelope. The obturator is formed as a transversely elongate outgrowth on the concave side of the funiculus and intervenes in the gap of the outer integument. During further development the inner integument produces several distal lobes, and the outer integument becomes bilobed. The exostome is a transverse slit with a middle notch, formed by the outer integument and the obturator. Presumed wide occurrence of the hood-shaped outer integument in primitive families suggests that it is a primitive state. The outer integument is compared with the ovuliferous sporophylls of the glossopterid and caytonialean seed ferns.