The long wait inside a seed

In 1879, botanist William James Beal buried bottles of seeds in sand at Michigan State University. The bottles were left uncorked and angled downwards so that water would not collect inside. They were intended to be unearthed at intervals and tested for germination. In 2021, a test of seeds from one of those bottles produced 20 seedlings of the genus Verbascum, more than 140 years after burial. ¹

That result did not establish a standard lifespan for seeds. It showed that some seeds in that particular experiment had survived that long. The rest had very different outcomes. It also left a problem Beal himself recognised: a seed that fails to germinate in a test is not necessarily dead. The experimenter may not have supplied the conditions that would allow it to grow. ¹

This uncertainty is central to the study of seeds. A living seed can remain outwardly unchanged while the conditions needed for germination differ from those of another species, another collection or another season.

What remains alive

Inside a seed is an embryo, an immature plant. In many species, food reserves help support its early development. Germination involves taking up water and resuming growth; the young root, called the radicle, emerges before the developing seedling establishes itself. Stored resources support this early growth before the seedling can depend on its own leaves. ²

Once that root has emerged, the plant faces a different set of demands. It must continue obtaining water and establish a working root system. Conditions that allow a seed to begin germinating may not keep a small seedling alive for long. Delaying the start can be useful in an environment with an unfavourable season ahead. ²

The delay is not a conscious choice. It results from the seed’s structures and physiology, which have evolved in relation to the conditions its species encounters. Some garden plants germinate readily after sowing; the seeds of other plants need a sequence of seasonal conditions. There is no single waiting period shared by all seeds. ²

Dormancy has a specific meaning

A dry seed on a shelf may simply lack the water it needs. Dormancy is more specific: a viable seed remains unable to germinate even when the immediate environmental conditions would otherwise be suitable. Knowing that a seed has not sprouted does not, on its own, tell you why. ³

Physical dormancy can come from a coat that prevents water entering. Physiological dormancy involves processes in the living tissues that restrict germination. Some species also disperse seeds whose embryos need further development. These are different problems, so a treatment that helps one kind of seed may do little for another. ³

Temperature history can matter as much as temperature on the day of sowing. Some seeds need a period of cold or warmth before they become able to germinate under suitable conditions. Light and daily temperature changes can also provide information about where a seed is lying. For a very small seed, germinating near the surface may be especially important because its reserves limit how far a shoot can grow before reaching light. ³

What smoke can signal

In some fire-prone environments, compounds in smoke can stimulate germination. Among them are karrikins, a family of molecules studied for their effects on seeds. The response is specific enough that scientists can investigate individual compounds rather than treating smoke as an unexplained general stimulus. ⁴

A 2009 experiment with Arabidopsis thaliana found that karrikins could promote germination of dormant seeds. The effect depended on light and on the plant’s ability to synthesise gibberellins, hormones involved in growth. The researchers also found variation in responsiveness among the Arabidopsis lines they tested. A compound could influence germination without overriding all the other conditions. ⁴

This matters when interpreting a flush of seedlings after fire. A response in one species or laboratory line does not establish that every seed needs smoke, or that smoke alone will make it germinate. The experiment instead shows how an environmental chemical can interact with the seed’s existing control systems. ⁴

Keeping seeds for the future

Seed banks try to preserve the capacity to grow, rather than encourage immediate germination. At Kew’s Millennium Seed Bank, collections suitable for conventional storage are dried, placed in airtight containers and kept at minus 20 degrees Celsius. Samples are tested for germination as part of checking whether a collection remains viable. ⁵

That approach cannot be applied to every species. Some seeds do not tolerate the drying or freezing involved in conventional banking. Their conservation needs other methods, and researchers investigate approaches including cryopreservation. The fact that one seed survives extreme storage says little about whether a different species will respond safely to the same treatment. ⁵

The practical question is often less straightforward than whether a seed looks intact. A collection needs an identity, a record of its treatment and evidence that it can still produce seedlings. A sealed jar can contain seeds in several states: living and ready to germinate, living but dormant, or no longer viable. A suitable germination test helps distinguish them, although interpreting a failure still requires care. ⁵