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REPRODUCTION IN FLOWERING PLANTS
A. Asexual Reproduction
Asexual reproduction in flowering plants is common. Many different seed plants utilize one of a number of different methods of this form of reproduction. There are several reasons why seed plants may find this form of reproduction advantageous. If the environment has been stable for many generations, variability may not be as essential to the survival of the species. Asexual reproduction which is not as complex and requires far less energy, would be preferable. When colonizing a new area, finding a mate for sexual reproduction may be difficult or impossible. If the environment is particularly harsh, the more delicate or susceptible organs or stages of sexual reproduction may not be able to survive. Many plants which inhabit such areas as deserts or arctic tundra only reproduce asexually. In this laboratory, you will examine various types of asexual reproduction, which are described in the following paragraphs.
Types of Asexual Reproduction
Plants such as the grasses, cattails and sedges produce underground stems or rhizomes. As these stems grow through the soil, they will periodically produce adventitious roots and a new above ground shoot. If the rhizome subsequently dies, a new separate plant will have been formed (Figure 6).
Figure 6: Plant Reproduction by the use of Rhizomes.
Tubers are actually modified rhizomes. They are formed in such plants as Irish potatoes. They develop when specialized stem branches grow down into the ground and swell up with starch containing cells. Buds on the tubers will grow into new plants. Examine the potato tuber and note the buds which are commonly termed "eyes" (Figure 7).
Figure 7: Plant Reproduction by the use of Tubers.
3. Runners (Stolons)
These are horizontally growing stems that produce few, if any, leaves. At the spot where a leaf would normally develop a node, these plants will produce adventitious roots down into the soil, and new above ground shoots. Examine the strawberry plant or spider plant. Note the runner and the new shoots (Figure 8).
Figure 8: Plant Reproduction by the Use of Runners/ Stolons.
A few seed plants such as the duckweed and Kalanchoe sp. produce miniature plants on the margin of their leaves. These drop off and develop into mature plants. The duckweed, which is an aquatic plant, reproduces almost entirely by this method. Observe the plantlets on demonstration (Figure 9).
Figure 9: Plant Reproduction by the Use of Plantlets.
Onions, chives and lilies over-winter in the form of a bulb. Each bulb has a very short stem which is surrounded by fleshy leaves. In the spring, the shoot apex begins to grow using the nutrients stored in the leaves. Examine the onion bulb and find the fleshy, storage leaves and ...
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