The Suspensor of Sciadopitys

Abstract

1. The early embryo of Sciadopitys shows two or three regions or tiers of cells which may develop into later stages. The cells of one of these regions elongate to form the prosuspensor; those of another represent embryo initials situated below the prosuspensor; and those of the third, which may be present, are rosette cells above the prosuspensor. A cap cell consisting of a terminal aborted embryo initial may be present, and other embryonic cells anywhere in the embryo system may become aborted. 2. As the prosuspensor cells become fully elongated, the embryo initials give rise to embryos which are pushed out on single-celled, primary suspensors. The early embryos pass through a stage in which an apical cell is recognizable. Rosette cells, when present, are embryo initials. These may give rise to embryos which are usually aborted in early stages. 3. Embryonal tubes are formed which reinforce the primary suspensor, thus giving rise to a multicellular secondary suspensor. 4. The potential output per archegonium is 12-28 embryos, which may develop independently for a time. If three eggs are fertilized, an embryo complex may be formed with several times this number of separate embryos. 5. Embryos may undergo budding and twinning in later stages; however, the seed usually contains only a single embryo which is fully matured with cotyledons. The number of cotyledons is usually two but occasionally three. 6. The stem tip is not organized until long after the cotyledons are formed. 7. The root cap is relatively short, and merges very gradually into the secondary suspensor. 8. The embryo of Sciadopitys is a type from which the embryos of the Cupressineae may have been derived; it also represents a type from which the embryos of the Taxodineae may have been derived. It has probably had a common origin with the embryo type represented by Cephalotaxus and certain podocarps, and appears to be more distantly related to the Abietineae.