Glossary - Seed Testing - page 325

Protoplasm . The essential complex living substance of cells on which all vital functions of nutrition, secre-
tion, growth, and reproduction depend.
Pseudocarpic fruit . A fruit consisting of one or more ripened ovules attached or fused to modiied bracts
or other nonloral structures (e.g., sandbur).
Pseudogamous apogamety . A type of diplospory (apomixis) in which the seed develops from some cell
of the diploid embryo sac other than the egg, but one in which the stimulus of pollination is required
before development will begin.
Pseudogamy . A type of apomixis in which the diploid egg cell develops into the embryo without fertiliza-
tion of the egg cell, although only after fertilization of the polar nuclei with one of the sperm cells from
the male gamete to form a normal triploid (3n) endosperm.
Pure seed content (percentage) . The percentage of each crop species that comprise 5% or more (by
weight) of a seed lot.
Quick test (seed testing) . A type of test for evaluating seed quality more rapidly than by standard labora-
tory tests.
Quiescence . The absence of growth, usually inferring the absence of environmental conditions favoring
growth; although dormant seeds are quiescent, quiescence is distinguished from dormancy, which
implies the inability to germinate even in the presence of environmental conditions favoring growth.
Raceme . A type of inlorescence in which the single-lowered pedicels are arranged along the sides of a
lower shoot axis.
Rachilla . The central axis of a grass loret.
Rachis . The main axis of a lower (or leaf).
Radicle . The rudimentary root of the seed or seedling that forms the primary root of the young plant.
Raphe . A ridge (seam), sometimes visible on the seed surface, which is the axis along which the ovule stalk
(funiculus) joins the ovule.
Receptacle . The basal structure to which the lower parts are attached, sometimes forming part of the
mature fruit, as in apple.
RST . The initials for Registered Seed Technologist, a designation for a private (commercial) seed analyst
who has passed tests and met other professional and academic requirements to merit a seal and the
designation of “Registered Seed Technologist.”
Rudimentary. Incompletely developed.
Samara. An indehiscent, winged fruit in which the seed coat is loose inside the pericarp (e.g., maple, ash).
Sampling. The method by which a representative sample is taken from a seed lot to be sent to a laboratory
for analysis. It is most commonly accomplished using triers, or seed probes, although hand methods
and mechanical sampling methods are also used.
Scariication. The process of mechanically abrading a seed coat to make it more permeable to water. This
process may also be accomplished by brief exposure to strong acids (e.g., sulfuric acid).
Schizocarp. A dry, two-seeded fruit of the carrot family that separates at maturity along a midline into two
mericarps. Each mericarp has a dry, indehiscent pericarp enclosing a loose itting ovule.
Sclerotium (pl. sclerotia). Compact mass of fungus hyphae usually with black outer surface and white
inner surface. Capable of remaining dormant for long periods of time and eventually giving rise to
fruiting bodies.
Scorpioid cyme. A determinate inlorescence in which the lateral buds on one side are sup pressed during
growth, resulting in a curved or coiled arrangement.
SCST . The initials of the Society of Commercial Seed Technologists, an organization of commer cial and
private registered seed technologists and seed analysts of the United States and Canada.
Scutellum. A shield-shaped organ of the embryo of grass. It is often viewed as a highly modiied cotyledon
in monocotyledons.
Seed . A mature ovule consisting of an embryonic plant together with a store of food, all sur rounded by a
protective coat.