Discussion
The results of the experiment were slightly unexpected. Although a general decrease in root lengths was shown as the black walnut solutions’ concentrations became higher, many of the results were inconsistent from each test group. For example, a seed from the control group, distilled water, had a root length of 22 mm. Some seeds that were saturated in black walnut fruit solution 1 (3.75% concentration) had roots longer than the roots from the control group. It was expected that the chemical contained in the solutions, called juglone, would inhibit the germination of the seed. The longest root resulted from a seed that was germinated in distilled water. Averages calculated from the root lengths of the seeds from each dish show that the black walnut fruit solution had a greater negative effect on the germination of the seeds than the black walnut leaf solution. This was expected because research prior to experimentation stated that more juglone is found in the nuts and fruit of the black walnut than in the leaves.
Standard deviation was calculated and revealed that none of the differences in the data were significant enough to conclude that black walnut fruit or leaves have a direct effect on the germination of tomato seeds. Standard deviation is a statistical test that shows how far apart the data points are from one another. A higher standard deviation indicates a larger range of data points. The standard deviation of the control group of the black walnut fruit solution tests was 36.33. The standard deviation of the least concentrated black walnut solution (.0375%) was 36.00. Black walnut fruit solution 2 (.375% concentration) had a standard deviation of 31.60. Black walnut fruit solution 3 (3.75% concentration) had a standard deviation of 21.67. For the black walnut leaf solutions, the control group had a standard deviation of 57.78, black walnut leaf solution 1 (.0375% concentration) had a standard deviation of 44.71, black walnut leaf solution 2 (.375% concentration) had a standard deviation of 30.11, and black walnut leaf solution 3 (3.75% concentration) had a standard deviation of 28.11. It is clear that in all tests, the range of the data points was very large.
This experiment took place over the course of four weeks. Originally, it was expected that the seeds' roots would be measured after one week, but it was found that more time was needed for the seeds to germinate. Data from the experiment, in general, showed that the longest root lengths resulted from the lower concentrated solutions. As the solutions became more concentrated, a general decrease in root lengths was shown, but the roots’ measurements in every test were not dramatically different from the others. After the completion of the experiment, the original hypothesis was rejected. Although the data showed a general pattern, it was not significantly different enough to conclude that black walnut leaf and fruit solutions have a direct effect on the germination of tomato seeds.
A factor that influenced the averages of each test and possibly resulted in error is that several seeds from each test did not start to germinate, so their root lengths were recorded as 0. The standard deviation was also affected by 0’s in the data because they caused for an even larger range of data, resulting in a higher standard deviation. The seeds that failed to germinate could possibly be the result of seeds that were defective or seeds that contained no embryo, also known as “empty seeds”. Of the 15 seeds measured from each test group, at least 3 of the seeds in each group did not germinate. The largest number of seeds in one group that did not germinate was 6. 6 seeds did not germinate in both the black walnut leaf and fruit solutions 1. Dishes containing black walnut fruit solution 3 and leaf solution 2 contained only 3 seeds each that failed to germinate.
If this project were to be repeated, it would be best to have more trials completed so that the results would be more accurate and clear. As a result of many of the seeds failing to germinate, the data and averages were affected. If many more seeds were tested, the data would most likely be more precise. Also, solutions with an even higher concentration of the black walnut fruit and leaves would be beneficial to this experiment. A reason that the results were not significantly different could be because the solutions did not contain a high enough concentration of juglone. Different types of seeds could be tested to see if the solutions would affect them differently than they affected the tomato seeds. Additionally, there are many other known allelopaths that could be tested to see which has the greatest impact on seeds’ germination.
Conclusion
The purpose of this experiment was to determine whether black walnut fruit and leaf solutions have an effect on the germination of tomato seeds. Results show that while there is a general pattern of decreasing root lengths of seeds as the solution becomes more concentrated, there is no significant effect of black walnut fruit and leaf solutions on the tomato seed’s germination. The allelopathic effects of black walnut trees did not impact the tomato seeds’ germination in this experiment. This information can be useful to gardeners or others working with plants because it indicates that the black walnut leaves and fruit do not inhibit the germination of tomato seeds if the concentration of the black walnut is low enough. Sensitive plants should not be grown in close proximity to the black walnut tree, but they have a chance of being unaffected by the black walnut if only a small amount of juglone is present.
As a result of the experiment, the question was asked: “Exactly how concentrated must a black walnut solution be for it to inhibit or stunt the germination of tomato seeds?” Also, how do other allelopaths of the same concentration affect the tomato seed’s germination? In future experiments, it is suggested that one should create black walnut solutions at higher concentrations to test, test different allelopaths’ effects on the tomato seed, or test black walnut solutions’ effect on other species of plants. Also, more trials would enhance the experiment and provide one with more accurate and precise results.