Grow a solid white daffodil and a solid yellow daffodil, each in a different pot. Growing the daffodils from bulbs rather than seeds will be quicker. After the daffodils bloom, brush one daffodil flower with a cotton swab or your fingertip to gather pollen. Spread the pollen on a flower of the other plant. Repeat this process, shifting pollen from one plant to the other plant. Allow the daffodil flowers to wilt. A seed pod will form behind the wilted flower. When the seed pod begins to shrivel and harden, harvest the seeds. Plant the seeds in a third pot. Wait for the seeds to grow and the daffodils to bloom to see what color combinations your new daffodil flowers possess. You can also experiment with other species of flowering plants. Note that it may take several years to witness the result of your cross-pollination experiment because daffodils grown from seeds do not produce flowers for the first two to three years. This is a long-term experiment.
Cut five lengths of stem from a full-grown geranium plant. Each length of stem should be 3 to 5 inches and should possess at least two leaves along the stem. Fill five pots with potting soil. Plant one stem in each of the pots. Vary how you plant the stems: plant one stem upright in a pot, one stem horizontal in an pot and so on. Place the pots in a sunlit location and add water as needed. Observe which stems grow most quickly and appear most healthy. Compare the new plants to the original plant.
Cut the base of several scions, or apple tree sucker shoots, into a wedge shape. Trim several rootstocks, or established apple tree saplings, down to 6 to 8 inches and make a cut, lengthwise, into the top of the rootstock. Insert the wedge of the scion into the cut in the rootstock. Seal the graft with grafting wax and cover with a layer of grafting tape. (Scions, rootstocks, grafting wax and grafting tape are all available at a well-stocked nursery.) Plant the grafted rootstocks into pots of quality soil. Plant a traditional apple tree sapling of the variety of the rootstock and one of the variety of the scions as well. Observe the growth of the traditional saplings and the grafted samples and compare their height, number of leaves and shape of leaves. Alternatively, you can perform this experiment with pear, plum and other fruit trees.
Purchase a full-grown gladiola from a nursery or grow a gladiola to maturity. Gladiolas grow in levels; the most mature blossoms will be located toward the base of the plants and the newest, or least mature, blossoms will be located toward the top of the plant. Pick blossoms from several levels of the plant and, one by one, dissect them. You will be looking for the pistil and the stamen. The pistil is the female reproductive system, which consists of the stigma, style and ovary. The stamen is the male reproductive system, which consists of the anthers and filament. It helps to have a diagram available as you dissect. Compare the various blossoms to determine which of the flowers' reproductive systems develops first.