Studies on Seed Germination and Subsequent Development in Orchidaceae

Abstract

Phases of seed germination and subsequent embryo devlopment in 47 species in Orchidaceae were examined.
1. Embryo after seed germination in 47 orchid species were categorized into 4 color groups : 1) white (32 species) ; 2) pale yellow (3 species) ; 3) pale green (7 species) ; and 4) green (5 species). White embryos change gradually from pale yellow to green during formation of protocorm, but in Cephalanthera falcata, Cremastra appendiculata and Gastrodia elata the embryos remain.
2. A single celled slender rhizoid develops from protruded part of protocorms in Chysis bractescens and Paphiopedilum insigne var. sanderae, but 610 rhizoids are devloped in the other species. No rhizoid was recognized in Gastrodia elata. Abundant root hairs were formed on roots of seedlings, except in Cephalanthera falacata. Furthermore, a part of root enlarged and produced bulbs in Habenaria radiata and Orchis graminifolia, but the shoots died gradually after formation of bulbs.
3. Rhizoids develop within 3 days after germination in (Bletilla striata) and 155 days in (Calanthe discolor × C. aristulifera). Root developed within 33 days after germination (Calanthe discolor and Bletilla striata) and 333 days (Calanthe tokunoshimensis). Rhizoid and root development are delayed in species having triangled protocorm showing whitish embryo at germination than in species having round and ellipsoidal protocorm. Futhermore, a tendency was observed that species which develop rhizoid fast also develop roots rapidly.
4. Terminal buds of protocorm elongated downward and formed a rhizome which kept elongating and branching in temperate Cymbidium. After elongation of the rhizome ceased, the terminal bud grew upward and differentiated into shoots and roots.
5. Among the 47 species examined, germinating embryos of terrestrial species from temperate and semi-tropical zones are generally whitish; they grew slowly and irregularly.
The germinating embryos of terrestrial and epiphytic species from temperate to tropical zones were pale yellow to green. They grew fast and uniformly after germination.
6. No correlation was found within a subfamily with respect to color and growth patterns of embryos and protocorm.