Seed dissection

Dissecting a specimen reveals internal features that can aid identification and may help determine if the specimen is a fruit or seed. After a specimen is dissected, distinguishing between the fruit wall and seed coat is easier. Note, though seeds from different families may have similar embryo shapes and sizes, combining these features with others selected in the key can narrow down the possible families of the specimen.

Seed in longitudinal section (top); illustration of a seed of the same genus in longitudinal section (bottom).
Seed in longitudinal section (top); illustration of a seed of the same genus in longitudinal section (bottom).
Three seeds in longitudinal section showing variation in embryo size and shape.
Three seeds in longitudinal section showing variation in embryo size and shape.

A seed should be dissected lengthwise through its thinnest side. As the seed may be unstable, hold the seed using forceps, tape, or very carefully with fingers. The narrowest edge of the seed should be placed on a firm surface. Then, using a single-edged razor blade or scalpel, cut through the middle of the seed with even pressure. Seeds longer than the razor blade may require two cuts or a scalpel. If possible, practice your technique before attempting on the specimen. A seed with a tough exterior can be softened by placing it in boiling water for a minute or so or letting it sit between damp paper towels for an hour or more (left too long and it could germinate!). After cutting open the seed, inspect the internal features to identify the embryo and nutritive tissues, and compare the embryo shape and size relative to the volume of the seed cavity to illustrations of these traits. Adding a small drop of Lugol’s iodine to the cut portion of the seed may help in differentiating these tissues.

About fruits and seeds