The physical change  of generations, of ferns, or  metagenesis is quite a unique    phenomenon. There are two different phases in one life cycle of            organisms which experience metagenesis. In one phase, spores are produced. In the other phase, sexual cells or gametes are produced. The spore-producing phase is called the sporophyte phase, and the gamete-producing phase is called the      gametophyte phase. The spores produced have a 2n or diploid chromosome         composition and the gametes produced have an n or haploid chromosome           composition.

When you observe ferns, you will see that there are groups of sporangia on the lower surface of the leaves (See Figure 1.8.). It means that the plant is in the sporophyte stage. The fern plants you are observing are members of a sporophyte generation. If the spores in the sporangia fall on a moist place, each will grow and be flatten into a heart-shaped structure called prothallium. it will produce male and female gametes.

In one lifecycle an alternation occurs  sbetween the sporophyte stage, in which spores with diploid chromosomes are produced, and the gametophyte stage, in which gametes with haploid chromosomes are produced. The alternation of the two stages is known as the alternation of generations or metagenesis.

Different species of plants grow differently. Some species grow into short plants with soft stems. They live for only a few weeks or a few months. Some other species grow tall and large, have wooden trunks, and live for years. What part of  the plants controls their growth?

            How do plants become longer? Observe the stem of a plant in Figure 1.11. On the stem you see two types of buds. At the tip there is a terminal bud, which is also known as an apical meristem. It determines the increase of plant length. Along the stem there are lateral buds, which are also known as side buds or             axillary buds. They can finally grow into branches, leaves, or flowers. Buds are the start of new growth and the points where they appear are nodes of growth. Some plant species have stems that keep becoming larger. In fact, some large stems like those found in wooden trees ( teak trees, and some forest trees) are even 1 to 2 meters in diameter. Why do they become so large? Stem enlargement is determined by the presence of a cambium. The cambium is       located between the xylem and phloem  and its function is to form new xylem and phloem .

Figure illustrates the increasing size of the diameter of the stern  stem. It is because the quantity of xylem and phloem increases in the same direction. It means that the cambium keeps producing new xylem and phloem. The stem tip is protected by epidermis on the outside. In any enlarged part of the stem  the epidermis  become               damaged due to the newly produced phloem. To replace it, a new protection is formed in the shape of cork tissues            Why new xylem and phloem arae continously produced? Do you know their function? They are vascular    tissues for transport. Xylem transports water and mineral    solutions from the roots to the sleaves. Phloem transports   photosynthesis products from leaves to all plant organs.      Because their function is important, these tissues are                 continuously produced. The larger the size of the stem, the more xylem and phloem  there are. Besides the stem, the roots’ also grow longer penetrate the soil. Where are the zones that determine root growth? To answer  this question.