We planted our bean seeds on Friday, Sept. 21. For some seedlings, the cotyledons are just breaking through the surface of the soil. For others, the first leaves are already developed and a dark green color. The seed package says the average germination time is 7-14 days, so we’ll have more sprouting in the next week. We should have fully grown plants with new beans to harvest in early November.
I marvel at the germination process each time I see it. As the cotyledons push out of the soil, the roots grow down into it. The roots absorb water and minerals from the soil while photosynthesis in the tender young green leaves traps the sun’s energy for use by the growing seedling.
“Everything growing from the earth, bless the Lord; praise and exalt him above all forever.” (Daniel 3:76)
Dissected seed showing the cotyledons, first leaves and first root.
First leaves developing between the cotyledons.
The dark green color shows that photosynthesis has started. The nutrients in the cotyledons are almost gone.
Students were amazed at how fragile the embryo was and how easily it fell out when the cotyledons were separated. Students summarized what they knew about requirements for seed germination. We also discussed why it was important to correctly and gently handle the germinating seeds and the seedlings. Students also wondered if the seeds would still germinate and grow if the embryo was separated from the cotyledons. Some came back to revisit this question when they developed their seed germination experiments a few classes later.
Classroom note: Iodine + starch produces a blue-black color and is used as an indicator for the presence of starch. Many bean seeds contain protein, so not all bean seeds will pick up the iodine stain. The blue-black color highlights the embryo, and makes it easier to distinguish the embryo from the cotyledon.
After observing and measuring dry bean seeds, groups of grade 5 students placed bush bean seeds in plastic bags with a moist paper towel in each bag. We hung the bags on a line near a window, so they had light as they germinated. Students observed them for 8 days. Each day they measured and recorded the growth of the seeds. Their first observations were that the seeds were enlarging after being in the bag with the moist paper towel. They also observed that seed coats were softer than they had been. By the 3rd day, the seed coats had split open. Next the embryo roots and stems appeared. The two cotyledons of each seed separated but continued to provide nutrients for the developing embryos. At the end of 8 days, some of the seeds were becoming moldy, so we decided not to plant all of them. Students were reluctant to dispose of the seedlings, so they took the young seedlings home. Students have reported that the plants are already forming new beans.
Place 2 bean seeds in a clear plastic bag with a damp paper towel. Make sure the bean can seen through the bag.
Write a hypothesis about what will happen.
Place the bag where it will receive sunlight.
Observe the results, measure the growth, draw and label the seed. Record daily for 5 days.