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Allelopathy: Effects of Volatiles from Crushed Plant Materials on Seed Germination and Growth.
Alleleopathy is defined by Oxford Reference Online as "an interaction involving two different species in which chemicals introduced into the en-vironment by one suppress the growth or reproduction of the other." In this experiment we tested whether the volatiles given off by garlic (Allium Sativum) and broccoli (Brassica oleracea) affected the germination of celery seeds. Thus if they inhibit the germination of the celery seeds we can say alleleopathy has occurred. Volatiles are the chemicals in the plant that easily escape the plant and evaporate into the surroundings. (www.dictionary.com)
As a group we assumed that volatiles from crushed garlic will inhibit the germination of the celery seeds and the volatiles from the crushed broccoli will not. Garlic has a strong offensive odor and if it repels vampires in folklore, its volatiles just may inhibit the germination of celery seeds. Ester compounds are mainly responsible for the aroma we smell in fruits according to Prof. Sarinsky. Maybe volatiles are somehow connected to these ester compounds. Thus, it was reasonable to assume that broccoli will not inhibit the germination of the celery seeds because broccoli barely gives off any odor, hardly as undesirable as garlic.
Materials & Methods
The materials needed for the experiment are: 4 petri dishes, 80 celery seeds, a garlic press, a clove of garlic, a small branch of broccoli, tape, marker, 4 pieces of filter paper, distilled water and some tin foil.
All four petri dishes were set up using the same first few steps. A circular piece of filter paper was fitted into each petri dish and pressed down so it served as the ground for the experiment. About three milliliters of distilled water was then poured into each dish. The filter paper soaked up most of it. Then using a small piece of tin foil, we carved a small dish for each of the petri dishes. After placing them in the center of the petri dish, twenty celery seeds were dispersed around the tin foil dishes onto the wet filter paper. The garlic was then pulverized using the garlic press and the confection was placed into one of the foil dishes. The branch of broccoli was the pulverized just the same and placed into one of the unoccupied foil dishes. The result was two petri dishes containing an empty foil dish, with twenty celery seeds dispersed around it on wet filter paper. One of the other two petri dishes contained mashed garlic in the foil dish and mashed broccoli was in the other. The control groups are the two petri dishes without the mashed specimen. The foil had to be used for control too because the only difference between a control group and experimental should be the experiment itself. The other two were the experimental group. The petri dishes were then covered with a lid, marked and sealed with tape. The tape was necessary for keeping the humidity of the atmosphere inside unaltered. The petri dishes were finally placed on a window sill where they all received the same amount of sunlight.
Observations were made everyday possible, in our case, four times a week. General size and quantity of the seeds were recorded. By general size we are talking about small, medium and large. We also dealt with nuisance variables which we identified as humidity, light and temperature. Humidity was controlled by sealing the petri dishes with tape to keep the water from escaping the environment. The petri dishes were placed on a window sill where they all had the potential to receive the same amount of sunlight. The temperature was stabilized by placing the petri in the same location, next to each other.
The seeds in the petri dish containing the mashed garlic had visible signs of germination, but their growth was stunted. They never grew anymore and instead started to die and rot by the end of the experiment. The seeds in the broccoli containing petri dish had a slower start compared to the control groups but caught up after about four days. The control groups and broccoli had a 100% seed germination by day #four. This information is displayed below.
Our hypothesis seems to have been proven correct except for a slight glitch in the germination of the celery seeds in the broccoli volatile environment. The volatiles from garlic do inhibit the germination of celery seeds and thus, alleleopathy does occur for the two. The slow start for the broccoli may or may not be do to alleleopathy, but if there was an agent in the volatiles of the broccoli that does inhibit the germination of celery seeds it must be in very minute amounts. Our experiment has better yeilds which are almost synonymous to repeating the experiment twenty times because we used twenty seeds for each petri dish.
Another experiment such as this can be conducted to verify our results. This time the celery seeds need to be much more visible. Once they began to sprout, the whole petri dish was green and distinguishing each individual seed was a bothersome task. Closer attention needs to be paid to the broccoli petri dish because our observations may have been faulted due to the sprouted celery seeds not being completely visible.
- "allelopathy" A Dictionary of Genetics. Robert C. King, William D. Stansfield and Pamela K. Mulligan. Oxford University Press, 2007. Oxford Reference Online. Oxford University Press. CUNY Central Offices. 28 January 2010 http://www.oxfordreference.com/view/ENTRY.html?subview=Main&entry=t224.e0208
- Thompson P.A. Germination of Celery (Apium graveolens L.) in Response to Fluctuating Temperatures OxFord University Press 1974. Online ISSN 146-2431
- Shimabukuro, Mary A. Haberman Vickie. An Aromatic Adventure with Allelopathy: Using Garlic To Study Allelopathy in the Classroom. American Biology Teacher; Apr2006, Vol. 68 Issue 4, p242-247
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