The Effects Of Garlic On Lettuce Seed Germination Biology Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

This research project is dedicated to determining the effect of garlic volatile on germination of lettuce seeds. Based on the background information referenced below as well as general knowledge of basic properties of plants we are going to hypothesize that the presence of garlic volatile has an inhibiting effect on germination of lettuce seeds, either completely destroying the young sprout or greatly impairing its growth potential. This hypothesis, once supported by experimental evidence, will bear a significant potential of predicting interaction between certain groups of plants. Such knowledge could be particularly useful in agricultural activity.

As a fairly recent biological concept, allelopathy was coined by Austrian plant physiologist Hans Molisch in 1938. However it was not until 1984 when E.L. Rice defined allelopathy as the effect of one plant (including microorganisms) on another plant through the release of a chemical compound into the environment. It is said that allelopathy can cause both stimulatory and inhibitory effect on the target plant, depending on the concentration of the compound (qtd. in Jefferson 275). The effects of allelopathy on germination and growth of plants may occur through a variety of mechanisms including reduced mitotic activity in roots and hypocotyls, suppressed hormone activity, reduced rate of ion uptake, inhibited photosynthesis and respiration, inhibited protein formation, decreased permeability of cell membranes and/or inhibition of enzyme action (qtd. in An 53).

Several sources rely on experimental data and research to state that allelopathic effect of one plant on another is largely dependent on such condition as rain, essentially providing a medium for allelopathic agent to get to its recipient faster and over a larger area. Affecting roots of plants via washing down of allelopathic chemical has been proven to inhibit target plant's growth or even chances of survival."Occurrence of autotoxicity and allelopathy . . . under field conditions may depend on two major factors: (1) size and density of plants; (2) soil and climatic conditions that control accumulation or disposition of allelopathic compounds" (Hegazy 11).

In spite of some unfinished research and skepticism in the scientific circles regarding the concept of allelopathy, I will be conducting experiment aimed to illustrate this phenomenon in general and support my hypothesis of inhibitory allelopathic effect of garlic volatile on germination of lettuce seeds in particular.


4 Petri dishes with covers

4 circles of Whatman filter paper

80 lettuce seeds

2 grams of garlic

Approximately 15ml distilled water

Masking tape

Aluminum foil


Triple beam balance


To conduct the experiment we used four Petri dishes lined with Whatman filter paper. In the middle of each dish we had placed aluminum foil base, circular in shape, approximately 30 mm in diameter and with walls raising from its outer perimeter up to approximately 10 mm. In the two experimental groups these bases were used as containers for garlic volatile. Twenty lettuce seeds were spread evenly across filter paper inside each of the dishes, and two out of four dishes were also recipients for garlic volatile in form of approximately 1 g of crushed garlic that was measured using triple beam balance and carefully placed in the aluminum base. Our goal was to measure the effect of garlic volatile (the independent variable) on germination of lettuce seeds (dependent variable). To ensure good statistical stability we doubled the experimental group that contained garlic as well as the control group with lettuce seeds and tinfoil base only. Thus we replicated our experiment to a total of 80 iterations, half of which belonged to experimental group and another half to control group.

All of the Petri dishes were sealed using a masking tape and placed into identical conditions for a total of two weeks. By doing so we were able to minimize the effect of nuisance variables such as temperature, humidity and light intensity on the results of the experiment, or to be more precise to impact both experimental and control groups equally by those factors in order to minimize any variations in conditions of the experiment to that of the independent variable. In our case all four dishes were placed on the same window sill, at approximately equal distance from both glass and the furnace grates. Each day of classes, measurements were taken from all four dishes, to include number of germinated seeds, sprout minimum and maximum length within each dish as well as changes in color, odor and appearance. This experiment should be easily repeatable due to the fact that it requires little space, few commonly available materials to set it up and easily obtainable abundant source of seeds and garlic.


Table 1 summarizes our experimental data. Refer to the legend below the table for code explanation and detailed notes:

Table 1

Note that no additional observations were available for the first day of reading due to the lack of comparative information. Test group codes are as follows:

E 1 = Experimental group (lettuce seeds with garlic volatile), set 1

E 2 = Experimental group (lettuce seeds with garlic volatile), set 2

C 1 = Control group (lettuce seeds without garlic volatile), set 1

C 2 = Control group (lettuce seeds without garlic volatile), set 2

The experiment lasted two weeks and for the clarity of visual representation, the graph portion is logically separated into two parts for each respective week. Week one encompasses data from observations 1 through 4 which were made from 07 Jan 2010 to 13 Jan 2010, and week two will be covered by observations 5-7, which were made from 14 Jan 2010 to 20 Jan 2010.

In addition to quantitative data gathered through the course of the experiment there were certain observations of odor and appearance that are noted in Table 1 under miscellaneous observations and are addressed in greater detail here. For example after all four dishes were sealed off to begin the experiment , the first reading indicated slight leakage of garlic volatile out of the dish marked as E 1. Though initially germinating and growing, lettuce seeds in both E 1 and E 2 dishes quickly degraded at the onset of week two of experiment, and during last readings were no longer viable for germination or sprout length reading. However they areas of filter paper underneath of what was lettuce sprouts became stained yellow with stain circles diffusing outwards as seed decay progressed.

The following graphs will illustrate the progression of seed germination and sprout length throughout the experiment grouped by week one and week two. The resulting graph will combine this progress and visualize the entire experiment from start to end.

Seed germination numbers through the course of week one

Sprout length through the course of week one

Seed germination numbers through the course of week two

Sprout length through the course of week two

Consolidated germination graph for the entire experiment

Consolidated sprout length graph for the entire experiment


Given the two separate isolated containers in form of Petri dish, each containing twenty seeds of lettuce for both experimental and the control groups, it can be stated with a fair degree of confidence that our group's experiment was reasonably protected from influence of nuisance variables and possesses a substantial enough number of total experiments complete to alleviate the statistical error component.

Before beginning the experiment, my prediction was that garlic would have a inhibitory allelopathic effect on the growth of other plants. After gathering information and data over the last two weeks, I have factual support of this hypothesis. The seeds inside Petri dish containing garlic grew no longer than one centimeter, compared to 3.5 centimeters in the control group. Additionally, there was fewer seed germination in the dish with garlic compared to the others. After three weeks, most of the sprouts with garlic had died, while the control group continued to grow and sprout leaves. As a result, my interpretation is that garlic does in fact have an inhibiting allelopathic effect on the germination and growth of lettuce seeds.

Let us review other minor factors that could have an effect on the results. As graphs suggest, both germination rate and sprout length were higher in dish coded E 1. This is the same dish that was detected to have a garlic odor leak during the first measurement. It is possible that leakage of garlic volatile outside of the dish space and resulting movement of air inside the dish allowed for more vital potential in that dish in its first and perhaps most important phase of germination as compared to a tightly sealed E 2. Inevitable rearrangement of seeds on the filter paper floor during measurements may have had an impact on the quality of germination and sprouting, however, as all eighty seeds in all four dishes were similarly handled it is safe to consider such influence equal for all the iterations. It is worth noting that our experimental Petri dishes were placed in the direct vicinity of other experimenter's setups and were exposed to potential random influence from those as well as other students present in the room when data was not being collected and the conditions could not be directly controlled. It is therefore possible that additional garlic volatile, presence of another experimenter's special control groups with carrots or simple chance of another student dropping our dish to the floor in our group's absence influenced the results to some extent. To alleviate this, a locked area access to which is only granted to the members of the research team could be used should this experiment be repeated by others to further examine and test the hypothesis.

It has been noted that crushed mass of garlic, located in the tinfoil bases of dishes E 1 and E 2, changed its color to dark brown by the end of the experiment. Additionally, when comparing the humidity condition between experimental and control groups it was easily noticeable that there was substantially less water in the experimental dishes, both in form of condensation and liquid within the filter paper. Therefore another conclusion that needs further verification is that garlic volatile could be absorbing massive amounts of water from its surroundings during the process of its evaporation, thus leaving less for the lettuce seeds in the dish and increasing its inhibiting effect. Perhaps this was the cause of rapid death and decay of the lettuce seeds in the experimental group as its onset coincided with garlic rapidly changing color.

The above results and conclusions also go in line with similar research conducted by many other scientists in the field of agriculture and biology. The hypothesis of inhibiting allelopathic effect of garlic on lettuce seeds is now supported and proven by own experimental data and facts.