The lettuce seeds



This investigation is to see the aromatic substance a chemical or plant aroma that goes into the air that affects other plants and organisms through diffusion; of garlic and broccoli will affect the growth of the lettuce seeds. Through Allelopathy; is "the study of effects of one plant on the growth of another plant through the release of low- molecular compound" (Rice, 1984). Does the aromatic substance produced by garlic and broccoli have an effect on the growth of the lettuce seeds? The prediction of this experiment is HA, garlic and broccoli will have an effect on the growth of the lettuce seeds. The dependent variable (what is being measured) of this experiment is the aromatic substance of both garlic and broccoli. The independent variable (what is being tested) is the growth of the lettuce seeds and the nuisance variable (how the experiment can be controlled) are water, lettuce seeds, light and temperature; by putting the same amount. Garlic (Allium Sativum) is said to be part of the onion family called Lillicaea. It is one of nature's versatile medicinal plants which is used to prevent heart attacks by thinning the blood, reduces fat in the blood and lowers blood pressure plus much more. Not only is garlic used medically, but is also used mythically such as keeping evil and vampires away for its strong odor called Allicin (an amino acid), when crushed. Broccoli doesn't have a strong odor than garlic and their isn't much information about it, but broccoli is said to come from the mustard or cabbage family called Cruciferae or Brassicacaea which produces flowers and interferes with the root growth of relative plants. Broccoli is also said to be a good source of dietary fiber and that reduces the risk of cancer. The experiment was divided into two groups, the "Experimental groups" which had garlic and broccoli and the "Control groups A and B" which had non-involvement of garlic and broccoli (aromatic substances). Both groups are given the same treatment; while only one group will have better results than the other.


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4 Petri dishes, 4 Filter papers, 2 Small pieces of aluminum foil, 20 Lettuce seeds on each Petri dish, 1 crushed clove of garlic, 1 Small piece of broccoli, and 3ml of water


  1. Put in 4 filter papers in each Petri dish.
  2. Pour in 3ml of water into each Petri dish.
  3. Put in 20 lettuce seeds separated from each other, making sure leaving the center empty.
  4. Fold aluminum into 2 small boats, putting them in each empty center inside the Petri dishes.
  5. Name each Petri dish; 2 Petri dishes should be named the "Experimental group" and the other 2 should be named the "Control group".
  6. One "Experimental group" will have 1 crushed glove inside the aluminum boat, while the other will have the broccoli. The "Control group" will be empty in the center.
  7. Close all Petri dishes with tape; check and water (3ml) when needed.


These procedures were made in this experiment to see and calculate the difference between both groups and both aromatic substances. In the methods each Petri dish needs to be named to observe the effects of the plants and what caused the changes. Each seed needs to be separated from one another for special growth. The steps and methods were carefully followed. There were no changes on the watering; it was in constant room temperature and light. Throughout this experiment in the "Experimental group" the aromatic substance (garlic and broccoli) had a great effect on the lettuce seeds. In the aromatic substance of garlic has shown a slower process in germination of the lettuce seeds. It seems that the aromatic substance of the garlic reduced the chlorophyll and growth of the seeds. The lettuce seeds were very short in length 1mm, throughout the observation process poor germination occurred; 9 out of 20. The rest were dark n pigmentation, they looked as they were dried out and just didn't germinate. In the aromatic substance of broccoli germination occurred much faster than the garlic. All the seeds germinated. The length of the seeds at first was approximately 1cm on 1/11/10. On 1/13/10 3 out of 20 stems were green and 3cm in length. All the other stems are at least a stem shorter of growth. The highest length the seeds reached was 5cm; but the pigmentation was very low. At the end the seeds didn't look healthy they the green chlorophyll was gone, the seeds showed more yellow and white in pigmentation. Broccoli in comparison to garlic showed more in length, structure, and color.

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The "Control group" was without the aromatic substances. In "Control group A" 13 out of 20 seeds germinated with 1cm in length. Throughout the observation the seeds weren't looking healthy. The seeds were dark in color, the length was still the same, no green color present; by 1/13/10 all seeds were germinated, but the growth is very slow. The seeds looked dull and weak. In "Control group B" all seeds germinated with 2cm in length. They looked healthier than "Control group A". The sprouts were green at the base coming out of the seeds.


My hypothesis stated that the garlic and broccoli would have an effect on the growth of the lettuce seeds. I believed that placing another plant in the space needed for another plant to grow would negatively affect its growth. As I proceeded to follow the experiment, I began to notice that my results were matching my hypothesis. As shown in the graphs we see that the allelopathy of the lettuce seeds with garlic had very little growth. This is a result to the garlic's aromatic substance called Allicin. Its strong odor reduced the lettuce's pigmentation and did not allow enough oxygen for the seeds to grow properly. The allelopathy with the broccoli showed a little more growth than with the garlic. Even though it had more growth, it was not enough for the lettuce to grow properly. Broccoli's residue has an effect of reducing root growth towards any plant in the Cruciferae family. Lettuce is known to be part of this family; therefore its growth was affected.

A further experiment would be a good idea because both of the controlled experiments differed in results. Control A and Control B were setup in the same exact environments; therefore their results should have been the same. If we proceeded to continue with another experiment we would be able to see what unnoticed variable affected these differences in results.


  • Ferguson, James J. "Allelopathy: How Plants Suppress Other Plants." EDIS - Electronic Data Information
  • Source of UF/IFAS Extension. July 2003. The Institute of Food and Agricultural Sciences (IFAS), Web. 10 Feb 2010. <>.
  • Rice, E.L. (1984). Allelopathy. 2nd. Edition. Orlando, FL: Academic Press, Inc.
  • "Information about the herb Garlic." Global Herbal Supplies. 1997. Global Herbal Supplies Pty Ltd, Web. 10 Feb 2010. <>.