Biology · Plant Reproduction, Signals & Responses

Seeds, fruits, dispersal and germination

One hundred seeds reach a patch of ground. Thirty later show radicle emergence. Calling the remaining seventy dead would skip several possible states. Some may be alive but dormant; others may lack suitable conditions. First decide which outcome was measured.

Plant Structure, Transport & Nutrition supplies meristems, tissue boundaries, water movement and source–sink transport. Development & Differentiation introduces changing cell identities; Meiosis & Patterns of Inheritance supplies haploid and diploid chromosome sets. The first lesson explains the plant life-cycle transition again before using n. Cell Regulation & Signalling is a useful return path for receptors and feedback, and Evolutionary Processes for the final lesson’s selection argument.

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By the end, you can

Separate seed development, dispersal, viability, dormancy, germination and establishment, and calculate a proportion using an explicit denominator.

Follow the ovule and its surroundings

A seed contains an embryo, protective tissues and resources that support early development; the location of stored resources differs among species. In flowering plants an ovule develops into a seed, while the ovary contributes to the fruit. Some fruits include substantial contributions from other floral tissues. A seed and a fruit consequently need separate outlines in a drawing.

Dispersal moves a seed or a seed-bearing structure away from its previous location. Wind, water, animals and the plant’s own structures can contribute. Arrival at a new site is not establishment. The seed may be eaten, damaged or deposited where later conditions are unsuitable. A fruit colour or a visit count alone does not measure the entire sequence.

An animal can both move and consume seeds. For a seed that survives movement, the outcome still depends on where it arrives and whether it later survives. Mutualism describes an outcome under specified conditions; it does not make every seed encounter beneficial. Separate numbers moved, numbers remaining viable and numbers recruited into the next generation.

A living seed can remain ungerminated

Viability means that a seed is alive and retains the capacity for the relevant development under appropriate conditions. Dormancy is a seed state that blocks completion of germination despite otherwise favourable conditions. Lack of water or another necessary external condition can also prevent germination in a nondormant seed. Absence of emergence by itself does not identify which explanation applies.

Germination includes reactivation and growth of the embryo; radicle emergence is a commonly used endpoint for its completion. Establishment is later: a seedling must continue functioning and survive in its setting. The constructed cohort uses radicle emergence as its stated endpoint and separately assigns whether nongerminated seeds are viable and dormant. Those assignments would need independent evidence in a real observation.

Genes and environment both affect dormancy. Work on DOG1 in Arabidopsis supplies one example of genetic contributions in a particular system. A gene name does not replace the conditions and tissue processes involved. Species differ in dormancy mechanisms and responses; the cohort below gives no recipe for overcoming dormancy.

Follow one hundred seeds through two endpoints

The later categories replace earlier histories rather than being added as new seeds.

Read the diagram in words

At the first endpoint, 30 germinated + 50 viable dormant + 20 nonviable = 100. At the later endpoint, the thirty become 18 established and 12 lost. The other 70 retain their assigned states. Germination is 30% of all seeds and 37.5% of the 80 viable seeds; establishment is 60% of germinated seedlings and 18% of all original seeds.

Original cohort: 100 seeds: 100

First endpoint
State at this endpoint	Number of original seed histories	Assigned viability
Germinated: radicle emerged	30	Viable
Viable and dormant	50	Viable
Nonviable	20	Nonviable

Later endpoint
State at this endpoint	Number of original seed histories	State at the first endpoint
Established seedlings	18	Germinated: radicle emerged
Lost after germination	12	Germinated: radicle emerged
Viable and dormant	50	Viable and dormant
Nonviable	20	Nonviable

Follow one hundred seeds through two endpoints
Question answered by the fraction	Numerator	Denominator	Fraction	Percentage
Germinated among all seeds	30	100	0.3	30
Germinated among viable seeds	30	80	0.375	37.5
Established among germinated seedlings	18	30	0.6	60
Established among original seeds	18	100	0.18	18

First endpoint
Later endpoint
Original cohort: 100 seeds
Seed histories

Constructed mutually exclusive states with viability and dormancy assigned independently; no natural rates.

Thirty of which seeds?

The teaching cohort ends with thirty germinated seeds, fifty viable dormant seeds and twenty nonviable seeds. The categories are mutually exclusive at the selected endpoint. Their sum is 100. Since the thirty germinated seeds were viable, the viable subset contains 30 + 50 = 80.

Relative to every seed received, the germination fraction is 30/100 = 0.30, or 30%. Relative to the independently assigned viable subset, it is 30/80 = 0.375, or 37.5%. The numerator stays thirty; the question changes the denominator. Neither value establishes that 37.5% is a natural species-wide germination probability.

The fifty dormant seeds are counted as viable, rather than as a second count of germinated seeds. No later germination time, seedling survival rate or intervention is assigned. Keeping the endpoint explicit makes the comparison useful without turning an invented cohort into a forecast.

Follow one hundred seeds through two endpoints

The later categories replace earlier histories rather than being added as new seeds.

Read the diagram in words

Original cohort: 100 seeds: 100

First endpoint
State at this endpoint	Number of original seed histories	Assigned viability
Germinated: radicle emerged	30	Viable
Viable and dormant	50	Viable
Nonviable	20	Nonviable

Later endpoint
State at this endpoint	Number of original seed histories	State at the first endpoint
Established seedlings	18	Germinated: radicle emerged
Lost after germination	12	Germinated: radicle emerged
Viable and dormant	50	Viable and dormant
Nonviable	20	Nonviable

Follow one hundred seeds through two endpoints
Question answered by the fraction	Numerator	Denominator	Fraction	Percentage
Germinated among all seeds	30	100	0.3	30
Germinated among viable seeds	30	80	0.375	37.5
Established among germinated seedlings	18	30	0.6	60
Established among original seeds	18	100	0.18	18

First endpoint
Later endpoint
Original cohort: 100 seeds
Seed histories

Constructed mutually exclusive states with viability and dormancy assigned independently; no natural rates.

Worked example

Continue the account into establishment

Suppose a later assigned census finds eighteen of the thirty germinated seedlings established, twelve no longer surviving, and no change to the fifty dormant and twenty nonviable seeds. The later account is 18 established + 12 lost after germination + 50 dormant + 20 nonviable = 100 original seeds. These are histories at a later endpoint, not additional seeds.

The conditional establishment fraction among the germinated seedlings is 18/30 = 60%. Relative to the original cohort it is 18/100 = 18%. Multiplying the two successive fractions, 0.30 × 0.60, recovers 0.18 because the second denominator is precisely the first stage’s thirty seedlings. It does not justify multiplying unrelated proportions from different cohorts.

Check your understanding

Can failure to emerge prove that a seed is dormant?
Show reasoning
No. A seed could be nonviable or lack necessary external conditions. Dormancy requires evidence of a viable seed whose state blocks germination under otherwise favourable conditions.
How can 30% and 37.5% both describe the same thirty germinated seeds?
Show reasoning
The first denominator is all 100 seeds; the second is the 80 independently assigned viable seeds. Different questions use different explicit subsets.
Eighteen seedlings establish after thirty germinate. What fraction of the original hundred is established?
Show reasoning
18/100 = 18%. The separate conditional fraction is 18/30 = 60% among germinated seedlings. The later account retains the other original histories without double-counting them.

What to carry forward

A seed’s movement, living state, germination and later survival answer different questions; name the endpoint and denominator.

References

Resources supporting this lesson’s explanations and examples.