Seed and Seedling Experiment
Seed and Seedling Experiment
Aims and Requirements: To learn the basic morphological structures and types of seeds and types of seedlings. Learn the methods of seed germination and understand the process of seed germination into seedlings.
(Source: Botany Laboratory Guide, Department of Plant Teaching and Research, School of Bioengineering, Shihezi University, compiled and illustrated by Feng Decheng, Li Xueyu, and Wan Zheng, second edition)
Operation method
Observation of seeds and seedlings
Materials and Instruments
Broad beans, kidney beans, peas, peanuts, castor or oleaginous seeds, corn, wheat, rice fruits; wheat, rice glume slices; soybean, kidney bean, peanut, pea, castor, wheat, rice, seedling of corn. Move I. Structure and types of seeds For more product details, please visit Aladdin Scientific website.
I-KI solution 1% Senna staining solution
Microscope Dissecting glass Petri dish Petri dish Blade Tweezers Dissecting needle Slide Coverslip Mirror paper Gauze
Seeds are the reproductive organs of seed plants that germinate to form seedlings.
1. Morphological structure of seeds of kidney bean, broad bean, castor etc.
We can choose the seeds of kidney beans, broad beans, soybeans and so on as materials, and soak the seeds in water 2-3 d before the experiment, so that they can be fully absorbed and softened, in order to facilitate the anatomical observation of the seeds.
(1) Morphological structure of bean seeds (Figs. 1 and 2): Take a bean seed that has been soaked and swollen. Seeds can be seen in a kidney shape, the seeds have a layer of leathery seed coat, the color of which varies according to the species. In the slightly concave side of the seed, there is a scar, it is the seed maturity and fruit detached from the traces left behind, known as the umbilicus. Dry the seeds, squeeze the two sides, water and bubbles can be seen from the umbilicus end of the overflow, here for the seed empty, that is, the ovule period of the bead hole, when the seed germination, the embryonic root is the first from the seed hole out of the breakthrough of the seed coat, so it is also known as germination holes. At the other end of the seed pore on the seed coat, there is a tumor-like protrusion at the far end, the distal end is the seed umbilicus, containing vascular bundles. Peel off the seed coat, the remaining part is the seed embryo, composed of four parts. The two plump petals are the cotyledons, and when the two cotyledons are broken apart, the cotyledons can be seen to be attached to the embryonic axis, and the buds at the upper end of the embryonic axis are the embryonic buds, and the two veined young leaves can be seen, and the young leaves can be carefully picked apart with a dissecting needle, and when observed with an enlarged microscope, the growth point of the embryonic buds and the protruding leaf primordia can be seen. At the lower end of the embryonic axis, the smooth cone exposed outside the cotyledons is the radicle.
(2) the morphology and structure of broad bean seeds: according to the observation of the anatomy of the bean seeds, take a grain of broad bean seeds have been soaked for observation, in the seed at one end of the black scar for the umbilicus, its structure and the bean seeds are basically the same, but the umbilicus on the no tumor-like protrusions, the embryonic bud on the young leaves without the bean clear.
(3) Morphological structure of castor seeds (Figure 3): take 1 castor seed, first observe its morphology and identify the seed ridges, caruncles and other accessory structures on the seed coat (seed holes are not obvious), and then gently break the hard seed coat with the flat end of the forceps. Peel off the testa and observe whether the testa is 1-layered or 2-layered. If 2 layers, what is the difference in texture between the outer and inner testa? With a razor blade or a dissecting needle, carefully divide the inner part of the seed coat into two halves along the direction parallel to the broad side of the seed, and observe with a magnifying glass, the milky white fleshy and plump part of the endosperm is the endosperm, and there are two very thin and obviously veined white "leaflets" immediately adjacent to the fleshy part of the cotyledons, and there is one leaflet at the corner of the "leaflet", and there is one leaflet at the angle of the "leaflet". There is a small protuberance at the corner of the "small leaves", which is the germ (only the growth point, not yet differentiated from the young leaves), and a short, thick, smooth protuberance below the germ is the radicle.
2. Morphological structure of the glumes of Gramineae
Corn, wheat and rice seeds were selected as materials. They were soaked in water for 2-3 d before the experiment. From the viewpoint of morphogenesis, these seeds are developed from the ovary, which should be a fruit with a thin pericarp that is not easy to separate from the seed coat and contains a seed. In the longitudinal section of the seed, the endosperm is visible within the testa, and the embryo is located in the endosperm at the base of the seed on one side (wheat, rice) or at the lower end of the base (maize). The above seed is a caryopsis (fruit) with a specialized structure.
(1) Morphological structure of the maize caryopsis (Figure 4): take a maize kernel for observation, its shape is rounded or malar, slightly flattened, at the lower end of the stalk, remove the stalk is seen on the pericarp there is a piece of black tissue, that is, for the umbilicus. Through the pericarp and seed coat can clearly see the embryo is located in the lower part of the broad side, with a razor blade perpendicular to the broad side of the glabrous fruit, along the embryo of the center of the longitudinal cut into two halves, with an enlarged mirror to observe its longitudinal section; it has a layer of thick skin, is the pericarp and the seed coat fusion formation. Within the pericarp and seed coat is mostly endosperm, in the dorsal base of a corner is the embryo, then add a drop of diluted iodine solution on the cut surface, visible endosperm part immediately turned blue-black, the embryo into orange, very clear (why?). The structure of the embryo can be seen as a tapered radicle with a radicle sheath; the upper part is the radicle with a radicle sheath; the shield between the radicle and the endosperm is the peltate (cotyledon), and the portion of the embryo between the radicle and the peltate and the peltate is the embryonic axis.
Then take a longitudinal section of the corn embryo under the microscope to observe the structure of the embryo in detail, distinguish the various components of the embryo, pay attention to observe the cotyledons and endosperm connected with a layer of larger, columnar arrangement of cells called epithelial cells, what is its function?
(2) the morphological structure of wheat (or rice) caryopsis (Figure 5): according to the methods and steps of observing maize caryopsis, observe the appearance of wheat caryopsis, wheat kernel is smaller than maize, ellipsoid, with a ventral groove, the tip of the unicellular epithelial hairs - fruit hairs, and other aspects of the maize is similar. Then take a longitudinal section of wheat and observe the structure of its embryo under the microscope, which is basically similar to that of maize, the main difference being that there is a small exosperm on the outer side of the embryonic axis of wheat.
The brown rice of rice is equivalent to a caryopsis, and its outer enveloping husk is equal to the palea lamina, and its embryo structure is similar to that of wheat embryo, with a single distinctly curved shape.
At the junction of the cotyledons (shields) and endosperm there is a neat layer of epithelial cells, and on the outer side of the embryonic cells opposite the cotyledons there is an upward protrusion called the exosperm.
Second, the process of seed germination and seedling formation, seedling type
Seed germination, that is, the seed embryo from a relatively static state into a physiologically active state, the embryonic cells undergo vigorous mitosis, and constantly produce new cells, the radicle breaks through the seed coat and grows downward to form the root system, while the germ also grows upward to form the stem and leaves, forming an autotrophic seedling process (Figure 6-8)
Observe seedlings of soybeans, kidney beans, peas, peanuts, castor beans, corn, wheat, and rice and identify the cotyledons, true leaves, epiblast, and hypocotyls of the seedlings against each of the diagrams below, as well as identifying cotyledon emergent seedlings and cotyledon retained seedlings.
III. Observation of the seedling formation process of seed germination
Under the guidance of the teacher, 7-10 days before the class in this experiment, students in groups to carry out experimental observation of seed germination. To observe the vegetable beans, soybeans, peanuts, peas, (or fava beans), rice, wheat (or corn) and other seeds, after the selection of soaking 2-3 d, so that it is fully absorbed by the expansion, and then sown into a pot of sand, soil or vantage point of wood chips, and watered with the appropriate amount of water (or put into the following pads with a filter paper, straw or gauze Petri dishes, watering with the appropriate amount of water to make the filter paper to maintain a moist state, covered with the lid of the Petri dish, the the petri dish into an incubator at 25 °C). Students will take turns each day in recording their observations, paying attention to which part of the embryo is the first to extend out of the seed coat when the seeds germinate? Do their cotyledons emerge? How do soybean and pea seedlings differ in form? Which part of the corn and wheat break through the pericarp first when they sprout? Which part emerges first? Do the cotyledons emerge? Note the changes in the seeds from day to day, as recorded in Table 1.
