Germination experiments investigate the conditions required for seeds to germinate and compare how differences in temperature, light, moisture, oxygen, and salt concentration affect germination rate and growth.
When suitable environmental conditions are present, seeds absorb water and resume internal metabolic activity. The radicle then breaks through the seed coat, followed by elongation of the young shoot. In general, germination is judged to have occurred when the radicle has emerged beyond a specified length.
In germination experiments, recording not only the final germination percentage but also the number of days required for germination, the uniformity of germination, and the elongation of roots and shoots allows the effects of different conditions to be evaluated in greater detail.
This article assumes an experiment using radish seeds to compare temperature, moisture, light, and salinity conditions, and summarizes the introduction, precautions, result items, example experimental values, calculations, sources of error, sample results, and discussion examples.
Note:
This article is a study reference for discussing results obtained in biology experiments at schools and universities. The experimental conditions and measurements shown are illustrative examples and are not actual results.
Do not touch moldy seeds or culture media with bare hands, and wash your hands after observation. Seal and dispose of moldy samples appropriately.
When using sodium chloride solutions or similar materials, check the concentration and amount used, and avoid accidental ingestion or contact with the eyes. Follow the laboratory manual and your instructor’s directions during actual experiments.
Basics of Germination
What Is Germination?
Germination is the process in which the embryo of a dormant seed resumes growth and the radicle or young shoot emerges through the seed coat. In experiments, a seed is often considered germinated when the radicle has emerged by at least 1–2 mm.
Main Conditions Required for Germination
- Water: required for seed imbibition and the resumption of enzyme reactions and substance transport
- Oxygen: required to obtain ATP through respiration
- Suitable temperature: required for enzyme reactions involved in germination
- Light or darkness: depending on the plant species, light conditions may promote or inhibit germination
Germination Percentage and Germination Speed
Germination percentage indicates what percentage of seeds ultimately germinated. Germination speed, on the other hand, indicates how quickly germination occurred. Even when the final germination percentage is the same, physiological responses may differ between conditions in which seeds germinate simultaneously within a short period and conditions in which germination occurs gradually over a longer period.
Main Items to Record in the Results
- Plant species used
- Seed cultivar and lot
- Number of seeds in each condition
- Treatment conditions
- Temperature
- Light conditions
- Type of water or solution
- Solution concentration
- Type of culture medium
- Culture period
- Germination criterion
- Number of newly germinated seeds each day
- Cumulative number germinated
- Final germination percentage
- Germination energy
- Mean germination time
- Germination speed index
- Radicle length
- Shoot length
- Total seedling length
- Number of ungerminated seeds
- Number of rotten or moldy seeds
- Number of replicates
- Mean and standard deviation
Example Experimental Conditions
| Item | Example condition |
|---|---|
| Plant material | Radish seeds |
| Number of seeds | 20 per condition |
| Medium | Petri dish lined with two sheets of filter paper |
| Added liquid volume | 5 mL per dish |
| Basic temperature | 25 ℃ |
| Light condition | Light or dark |
| Observation period | 7 days |
| Germination criterion | Radicle emergence of at least 2 mm |
| Replicates | 3 per condition |
Example Experimental Values
Daily Germination at 25 ℃ with Distilled Water
| Observation day | Newly germinated seeds | Cumulative germinated seeds | Cumulative germination (%) |
|---|---|---|---|
| Day 1 | 2 | 2 | 10 |
| Day 2 | 8 | 10 | 50 |
| Day 3 | 6 | 16 | 80 |
| Day 4 | 2 | 18 | 90 |
| Day 5 | 1 | 19 | 95 |
| Day 6 | 0 | 19 | 95 |
| Day 7 | 0 | 19 | 95 |
Comparison of Germination by Temperature
| Temperature (℃) | Germinated seeds (/20) | Final germination (%) | Mean germination time (days) | Mean radicle length (mm) |
|---|---|---|---|---|
| 10 | 12 | 60 | 5.1 | 18.4 |
| 20 | 18 | 90 | 3.0 | 39.6 |
| 25 | 19 | 95 | 2.7 | 48.2 |
| 30 | 17 | 85 | 2.5 | 42.7 |
| 40 | 4 | 20 | 4.8 | 7.3 |
Comparison by Moisture Condition
| Moisture condition | Added liquid | Germination (%) | Mean radicle length (mm) | Observation |
|---|---|---|---|---|
| No addition | 0 mL | 0 | 0.0 | Seeds showed almost no change |
| Low | 2 mL | 70 | 28.5 | Filter paper dried during the experiment |
| Optimal | 5 mL | 95 | 48.2 | Good germination and elongation |
| Excessive | 15 mL | 55 | 19.8 | Seeds were submerged and some rotted |
Comparison by Light Condition
| Condition | Germination (%) | Mean radicle length (mm) | Mean shoot length (mm) | Shoot color |
|---|---|---|---|---|
| Light | 95 | 48.2 | 31.5 | Green |
| Dark | 90 | 46.7 | 52.8 | Yellowish white |
Comparison by Sodium Chloride Concentration
| NaCl concentration (%) | Germinated seeds (/20) | Germination (%) | Mean radicle length (mm) | Root elongation relative to control (%) |
|---|---|---|---|---|
| 0.0 | 19 | 95 | 48.2 | 100 |
| 0.5 | 18 | 90 | 39.7 | 82.4 |
| 1.0 | 15 | 75 | 26.4 | 54.8 |
| 1.5 | 10 | 50 | 12.1 | 25.1 |
| 2.0 | 4 | 20 | 4.8 | 10.0 |
Example Replicate Measurements
| Condition | Trial 1 (%) | Trial 2 (%) | Trial 3 (%) | Mean germination (%) |
|---|---|---|---|---|
| Distilled water | 95 | 90 | 95 | 93.3 |
| NaCl 0.5% | 90 | 85 | 90 | 88.3 |
| NaCl 1.0% | 75 | 70 | 80 | 75.0 |
| NaCl 1.5% | 50 | 45 | 55 | 50.0 |
Calculation Methods
Germination Percentage
If 19 of 20 seeds germinated:
Germination (%) = Number of germinated seeds ÷ Total number of seeds × 100
= 19 ÷ 20 × 100
= 95%
Cumulative Germination Percentage
If 16 seeds had germinated by Day 3:
Cumulative germination (%) = Cumulative germinated seeds ÷ Total seeds × 100
= 16 ÷ 20 × 100
= 80%
Germination Energy
Germination energy is the percentage of seeds that have germinated by a specified early time point. If Day 3 is used and 16 seeds have germinated:
Germination energy (%) = Seeds germinated by specified day ÷ Total seeds × 100
= 16 ÷ 20 × 100
= 80%
Mean Germination Time
Mean germination time is calculated using the number of newly germinated seeds on each day.
Mean germination time = Σ(day × newly germinated seeds that day) ÷ Total germinated seeds
For 2 seeds on Day 1, 8 on Day 2, 6 on Day 3, 2 on Day 4, and 1 on Day 5:
= (1×2 + 2×8 + 3×6 + 4×2 + 5×1) ÷ 19
= 49 ÷ 19
≈ 2.58 days
Germination Speed Index
The germination speed index gives greater weight to seeds that germinate earlier.
Germination speed index = Σ(Newly germinated seeds each day ÷ Day of germination)
Using the example values:
= 2/1 + 8/2 + 6/3 + 2/4 + 1/5
= 2 + 4 + 2 + 0.5 + 0.2
= 8.7
Mean Radicle Length
If the radicle lengths of five seedlings are 45, 49, 51, 47, and 49 mm:
Mean radicle length = (45 + 49 + 51 + 47 + 49) ÷ 5
= 48.2 mm
Root Elongation Percentage
If the mean radicle length is 48.2 mm in the control and 26.4 mm in the 1.0% NaCl treatment:
Root elongation (%) = Mean radicle length in treatment ÷ Mean radicle length in control × 100
= 26.4 ÷ 48.2 × 100
≈ 54.8%
Germination Inhibition Percentage
If the control germination percentage is 95% and the 1.5% NaCl treatment is 50%:
Germination inhibition (%) = (Control − Treatment) ÷ Control × 100
= (95 − 50) ÷ 95 × 100
≈ 47.4%
Mean
If germination percentages in three replicates are 95, 90, and 95%:
Mean = (95 + 90 + 95) ÷ 3
= 93.3%
Standard Deviation
s = √{Σ(xi − x̄)2/(n − 1)}
The standard deviation calculated from germination percentages of 95, 90, and 95% is approximately 2.89%.
Main Sources of Error
| Source of error | Effect on measurement | Likely effect on results | Improvement |
|---|---|---|---|
| Differences in seed quality | Differences in dormancy, aging, or damage | Germination varies even under identical conditions | Use seeds from the same cultivar and lot |
| Too few seeds | Each seed has a large effect | Large fluctuations in germination percentage | Increase seed number and replicates |
| Ambiguous germination criterion | Judgment differs among observers | Germination count may be over- or underestimated | Set a criterion such as radicle ≥2 mm |
| Variation in observation time | Germination day is assigned inconsistently | Mean germination time becomes inaccurate | Observe at the same time each day |
| Variation in added liquid | Moisture conditions differ | Germination and root length vary | Add a fixed volume with a pipette |
| Drying of filter paper | Water uptake stops and elongation is inhibited | Germination and root length decrease | Check moisture daily |
| Excess moisture | Oxygen around seeds becomes limited | Lower germination and more decay | Do not completely submerge seeds |
| Temperature fluctuations | Enzyme reaction rates change | Germination time varies | Use a temperature-controlled incubator |
| Position differences within the dish | Light, temperature, and moisture are uneven | Germination differs by position | Arrange seeds evenly |
| Seeds touching each other | Local moisture and oxygen conditions change | More decay and tangled roots | Keep seed spacing uniform |
| Error in salt concentration preparation | Osmotic conditions differ from intended values | Concentration effects are misjudged | Weigh and make up solutions accurately |
| Concentration by evaporation | Salt concentration rises during culture | Germination and growth become increasingly inhibited | Cover containers with lids |
| Mold or bacterial growth | Seeds are damaged and oxygen/nutrients are consumed | Lower germination and more decay | Use clean equipment |
| Curved roots during measurement | Straight-line distance differs from actual length | Root length is underestimated | Measure curved length on images |
| Root damage | Elongation stops prematurely | Mean root length decreases | Do not move seeds during observation |
| Light leakage | Light enters the dark treatment | Differences between light and dark conditions become smaller | Cover completely with light-blocking material |
| Handling of ungerminated seeds | The mean changes depending on whether zeros are included | Interpretation of the mean changes | State the calculation method clearly |
| Observation period too short | Late-germinating seeds are missed | Final germination is underestimated | Observe until germination count stabilizes |
Why Water Is Necessary
When a seed absorbs water, its cells swell and dormant enzymes begin to function. Stored substances are broken down, supplying materials and energy needed for embryo growth, allowing germination to proceed.
Why Excess Water Reduces Germination
When seeds are submerged, less air surrounds them and oxygen supply becomes limited. Because ATP production through respiration is necessary during early germination, oxygen deficiency suppresses germination and root elongation.
Why Germination and Growth Are Highest at a Suitable Temperature
Germination involves many enzyme-mediated processes, including breakdown of stored materials, respiration, cell division, and cell elongation. At a suitable temperature, these reactions proceed efficiently, resulting in faster germination and better root and shoot growth.
Why High Temperature Reduces Germination
At high temperatures, enzymes and cell membranes may be impaired and respiratory consumption may increase. Water evaporation and microbial growth may also accelerate, potentially reducing germination.
Why Higher Salt Concentrations Inhibit Germination
As the salt concentration of the external solution increases, its water potential decreases, making it more difficult for seeds to absorb water. In addition, ionic stress from sodium and chloride ions can affect enzymes and cell membranes, reducing germination and root elongation.
Why Shoots Become Longer in Darkness
In darkness, etiolated growth occurs, causing shoots to elongate rapidly in search of light. Shoots therefore become longer, but chlorophyll formation is insufficient and they remain yellowish white.
Example of How to Write the Results
Twenty radish seeds were cultured on filter paper for seven days to investigate the effects of temperature, moisture, light, and sodium chloride concentration on germination.
At 25 ℃ with distilled water, 19 seeds germinated, giving a final germination percentage of 95%. Mean germination time was 2.58 days, and germination energy by Day 3 was 80%.
Among the temperature treatments, 25 ℃ produced the highest values, with 95% germination and a mean radicle length of 48.2 mm. Germination was delayed at 10 ℃, while germination fell to 20% at 40 ℃.
Among the moisture treatments, the 5 mL treatment produced the best germination and root elongation. In contrast, no seeds germinated without added water, and some seeds decayed in the 15 mL treatment.
As NaCl concentration increased, both germination and radicle length decreased. At 2.0% NaCl, germination was 20% and root elongation relative to the control was 10.0%.
Points to Address in the Discussion
- Which condition produced the highest germination percentage?
- Did germination percentage and germination speed show the same trend?
- What characteristics were associated with shorter mean germination times?
- Why did seeds fail to germinate without water?
- Why did excessive moisture reduce germination?
- Why did temperature alter germination percentage and root length?
- Why did germination decrease at high temperature?
- How did light affect germination, root length, shoot length, and color?
- Why were shoots longer in darkness?
- Why did increasing salt concentration inhibit germination and root elongation?
- How does including or excluding ungerminated seeds from mean root length affect the result?
- How did mold, drying, temperature variation, and seed quality affect the results?
Discussion Example
In this experiment, radish seeds were used to investigate how temperature, moisture, light, and sodium chloride concentration affect germination.
At 25 ℃ with distilled water, 19 of 20 seeds germinated, giving a final germination percentage of 95%. Germination began on Day 1, and 16 seeds had germinated by Day 3, giving a germination energy of 80%.
The mean germination time was 2.58 days, indicating that many seeds germinated on Days 2–3. Calculating mean germination time in addition to final germination percentage made it possible to evaluate germination speed.
In the temperature treatments, germination increased and mean germination time decreased as temperature rose from 10 ℃ to 25 ℃. Germination requires enzyme reactions involved in breakdown of stored substances, respiration, cell division, and cell elongation.
At 10 ℃, enzyme reactions and metabolism were slower, so germination required more time and many seeds may not have germinated within the observation period.
At 25 ℃, germination was 95% and mean radicle length was 48.2 mm, suggesting that this temperature was suitable for germination and early growth under the experimental conditions.
At 30 ℃, germination occurred slightly earlier, but final germination and radicle length were lower than at 25 ℃. Although metabolic rate increased with temperature, some seeds may have experienced heat stress.
At 40 ℃, germination fell to 20% and radicle length was only 7.3 mm. High temperature may have affected enzymes and cell membranes involved in germination, interfering with normal metabolism and cell elongation.
In the moisture treatments, no germination occurred without added water. Seeds resume enzyme activity after imbibition and break down stored materials for embryo growth, so germination could not proceed without water.
With 2 mL of water, germination was 70%, lower than with 5 mL. The filter paper dried during culture, likely causing insufficient water uptake and suppressing germination and root growth.
In contrast, seeds were submerged in the 15 mL treatment and germination fell to 55%. Excess water reduces the air surrounding seeds and limits the oxygen required for respiration.
During early germination, before photosynthesis begins, the embryo must break down stored materials through respiration to obtain ATP. Oxygen deficiency therefore likely inhibited germination and elongation.
There was little difference in germination between light and dark treatments, suggesting that light had a relatively small effect on germination itself in the radish seeds used here.
However, shoot length was 52.8 mm in darkness, compared with 31.5 mm in light, and shoots grown in darkness were yellowish white.
In darkness, etiolated growth causes stems and shoots to elongate rapidly in search of light. Without light, chlorophyll formation is insufficient, explaining why the shoots did not become green.
As sodium chloride concentration increased, both germination and mean radicle length decreased. Germination was 95% and mean radicle length was 48.2 mm at 0% NaCl, whereas at 2.0% NaCl germination was 20% and mean radicle length was 4.8 mm.
Under high-salt conditions, the water potential of the external solution decreases, making water movement into seeds more difficult. This delays seed imbibition and swelling and makes the metabolic reactions required for germination more difficult.
In addition, sodium and chloride ions may affect cell membranes, enzymes, and ionic balance, suppressing cell division and elongation after germination.
Radicle length declined markedly even at lower salt concentrations than germination percentage, suggesting that post-germination root elongation was more sensitive to salt stress than the initiation of germination.
One source of error was variation in seed quality. Even under identical conditions, differences in dormancy, maturity, deterioration during storage, or damage to the seed coat can alter whether and how quickly seeds germinate.
Furthermore, with only 20 seeds per condition, each seed represents 5 percentage points of germination, so even a small number of defective seeds can substantially affect the result. Increasing both seed number and the number of replicates would reduce the influence of chance.
The germination criterion also affects the calculated germination percentage. Counting seeds whose coats have merely split versus counting only seeds whose radicles have reached a specified length can produce different results.
In this experiment, germination was defined as radicle emergence of at least 2 mm. The same criterion should be used when comparing experiments.
Mean radicle length also differs depending on whether ungerminated seeds are included as 0 mm or excluded. When evaluating overall performance including germination ability, ungerminated seeds may be treated as zero; when comparing growth only after germination, only germinated seedlings may be included. The calculation method should be stated according to the purpose of the experiment.
To improve measurement accuracy, seeds from the same lot should be randomly assigned to treatments, seed number and replicates should be increased, and liquid volume, temperature, observation time, and germination criteria should be standardized.
Overall, radish seed germination required an appropriate amount of water, oxygen, and a suitable temperature. Germination and early growth decreased under water deficit, excess water, high temperature, and high salt concentration. Light affected shoot morphology and color more strongly than germination percentage.
Discussion Example When Germination Was Low in All Conditions
Low germination in all conditions may have resulted from poor seed storage, old seeds, incomplete release from dormancy, drying of the culture medium, temperatures outside the optimal range, or damage caused by mold or bacteria.
Discussion Example When Germination Was Slow Even in the Control
Slow germination even in the control may have been caused by low incubation temperature, insufficient seed imbibition, inadequate oxygen supply, seed dormancy, or variation in seed quality.
Discussion Example When Germination Remained High in Concentrated Salt Solution
If germination remained high even in concentrated salt solution, the plant species may have relatively high salt tolerance. However, errors in solution preparation, accidental substitution with distilled water, evaporation or dilution, and the germination criterion should also be checked.
Discussion Example When Measurements Varied Widely
Large variation among measurements may have resulted from differences among replicates in seed quality, water uptake, position within the Petri dish, moisture level, mold growth, observation time, germination judgment, or root measurement method.
Summary
Germination is the process in which a seed absorbs water, resumes metabolism, and the radicle or young shoot emerges through the seed coat.
Germination requires an appropriate amount of water, oxygen, and a suitable temperature. In some plant species, light conditions can also promote or inhibit germination.
In germination experiments, evaluating germination energy, mean germination time, germination speed index, and root and shoot elongation in addition to final germination percentage provides a more detailed assessment of treatment effects.
Insufficient water prevents adequate imbibition and metabolism, while excessive water can cause oxygen deficiency. High salt concentrations inhibit germination and root elongation through osmotic and ionic stress.
In the discussion, factors such as temperature, moisture, oxygen, light, salt concentration, seed quality, germination criteria, observation period, mold, and replicate number should be related to changes in germination percentage, germination speed, and root length.
