Anatomy of the Cannabis Seed – Achene, Embryo and Storage Reserves

What the trade calls a seed is botanically a fruit. The cannabis achene encloses a single seed within a hard, indehiscent fruit wall, the pericarp. The distinction is not pedantry: the hull that protects the seed is the same body that has to be overcome at germination, and its toughness has a say in whether an old stock still emerges. The structure described below comes from electron microscopy of a fibre cultivar.

Fruit wall and size

The fruits examined measured 4 to 5 millimetres long and 3 to 4 millimetres across. Across cultivars, figures of 2 to 6 millimetres in length and 2 to 4 millimetres in diameter are reported, though as a citation of older literature rather than a measurement made in the same study. Beneath the pericarp lies the testa, the papery seed coat. Together the two form the mechanical envelope, and their structure and rigidity help govern germination.

Position of the embryo

The embryo sits curved into a U shape inside the fruit. The tip of the radicle and the cotyledons both point towards the stylar end, where a cavity in the distal region holds the radicle. That arrangement explains what happens at germination: the radicle emerges at the stylar end and splits the hull into two halves that stay joined at the base. Open a fruit and one end offers markedly more resistance than the other.

Endosperm and storage reserves

Unlike in cereals, the endosperm of a mature cannabis seed is no longer a nutritive tissue of any weight. It has shrunk to a narrow peripheral zone and acts mainly as a further mechanical barrier. The reserves sit in the cotyledons instead. Composition is given as roughly 18 to 30 % protein, 30 to 40 % oil and 25 to 34 % carbohydrate, with the globulin edestin as the main storage protein at 67 to 75 % alongside 25 to 37 % albumin. These ranges too are values carried over from the nutritional literature, not measurements on the material described.

Oil bodies and protein bodies under the microscope

Cotyledon cells are packed with two types of organelle. Protein bodies measure 2.5 to 3.5 micrometres across, the oil bodies surrounding them 0.7 to 1.8 micrometres. Each oil body is bounded by a half membrane carrying proteins that act as emulsifiers and keep the droplets apart. While the seed is dormant they do not coalesce.

That picture changes as germination begins: rough endoplasmic reticulum approaches the oil bodies, their margins become undulated, and eventually they fuse. The reading that proteins formed at this reticulum pass through the half membrane and cleave the emulsifiers there rests on morphological observation and has no biochemical proof. What was absent is equally notable: no peroxisomes or glyoxysomes were observed in these cells, although in other species they carry the breakdown of storage oil.

What the structure means in practice

Two things follow directly. First, the resistance at germination sits in the pericarp and testa rather than in the embryo, which is why complete removal of the fruit wall recovers measurable germination in weak seed lots; that is covered in the article on improving germination. Second, a decoated seedling no longer breaks the remaining testa with its root tip but by elongation of the hypocotyl and cotyledons, which makes it more sensitive to an overly wet germination medium at that stage.