Sexual reproduction of Engelmann spruce ( Picea engelmannii)

Abstract

The anatomy and phenology of sexual reproduction of Picea engelmannii Parry from three sites near Prince George, B.C., has been described. The developmental stages at the higher elevation and consequently colder site lagged by 1–2 weeks compared with the lower elevation sites. Pollen mother cells underwent meiosis in mid-May and the five-celled pollen was shed from the end of June to the 1st week of July. The ovules went through the winter rest in the megaspore mother cell stage. The latter underwent meiosis in mid-May to form linear tetrads. The integument was initiated in the postdormancy stages and developed two micropylar prongs which seem characteristic of the genus. The nucellus showed a massive nucellar cap and a pollen chamber formed by the degeneration of cells. The young female gametophyte was surrounded by a spongy tissue which persisted at the chalazal end where the megaspore wall was thickest. The female gametophyte usually bore two archegonia which were fertilised in mid-July (3 weeks after pollination). The embryo developed over the next 3 months. Two main factors which contribute to ovule abortion are failure of pollination and degeneration of embryo during early development.