Cactus reproduction

When    talks about reproduction, we must make a clear distinction between asexual reproduction by cutting or grafting and sexual reproduction by seed. Plants with exactly the same genetic genes as the female parent can be obtained through asexual reproduction, and the offspring are in fact a part separated from the female parent. When cutting cuttings, the fresh cross-section of cuttings is moist because many cells gush out after being cut. In order to prevent the plant from evaporating too much water after injury, the wound will soon produce callus and seal it. After the cross section and the nearby cell layer are dry, the wound stops evaporating water. After a few days, the surviving cells under the cross section will form a cork layer, and the cross section will be completely healed and closed. Any living cell can produce a cork layer if necessary, but only certain cross-sectional cells can produce roots, a small number of cells in the vascular bundle-the so-called cambium. The cambium lies between the xylem and the sieve tube, and the latter two are produced by the division of cambium cells. Because the vascular bundles in the middle of the plant are arranged in a finger ring, the roots of the cuttings are usually arranged in a bad shape. The grafting rule is completely different from the rod insertion method. After the grafting interface section is completely dry, the graft can not survive, and the graft should be installed as soon as possible while the cross-section cells of the rootstock and the graft are still alive, so as to make the stone tree closely match with the graft. The grafting operation is actually not very difficult.

The success of grafting also depends on the cell viability of the cambium. Grafting will be successful only if the cambium (or at least part of it) of the rootstock and graft can heal.

The picture shows: cactus seedlings

If    uses seeds for sexual reproduction, the genetic characteristics of the two parent plants will be recombined. The plant that provides pollen is called the male parent, while the plant that produces seeds is called the female parent. The offspring will not be exactly the same as any of their parents. Because of the different homozygosity of the parents, the offspring are colorful.

   already knows something about the structure and pollination of cactus flowers. But the true conception of a flower can only be seen through a microscope. Pollen consists of many tiny pollen grains. There is a hard layer on the outside of the pollen grain, which is mainly composed of spore pollen with strong disease resistance. This layer of exoskeleton is formed by the outward separation of cells, just like the cuticular membrane formed by the separation of epidermal cells. Under the microscope, many pollen grains show beautiful patterns. The life span of pollen grains is often only a few days, but they can survive for a longer period of time in cool and dry conditions, which we will elaborate on in cactus cultivation. When the pollen grains fall on the appropriate stigma lobes, the exosperm will crack in a thin wall (germinating pore), the inner wall of the cellulose below will begin to expand, and gradually produce a pollen tube from the pollen grain. At this point, the pollen grains only need the mucus secreted in the stigma lobes to germinate.

There is a so-called "growth nucleus" (vegetative nucleus) at the top of    pollen tube, which can control the growth of pollen tube. With the growth of the pollen tube, the "growth nucleus" (vegetative nucleus) also moves forward, so that the pollen tube shows the characteristics of apical growth. The pollen tube reaches the ovule in the ovary through the style. The ovule has two layers of integument, and the integument has a small pore (micropyle).

The pollen tube enters the embryo sac from the micropyle. The germ cell at the top of the pollen tube divides into two sperm, one of which binds to the egg cell close to the micropyle. This process is called fertilization. At this time, the genetic characteristics of the male parent and the female parent are recombined. The other sperm binds to the secondary nucleus. The phenomenon that two sperm bind to the egg cell and the secondary nucleus respectively is called double fertilization. After double fertilization, the ovule develops rapidly. Fertilized egg cells develop into embryos, that is, tiny plants with radicles, hypocotyls and cotyledons, sperm combined with secondary nuclei develop into endosperm nuclei, then develop into seed vegetative tissue (endosperm), and integuments develop into hard seed coats. These are the most important components of seeds. In the process of seed ripening, the endosperm is gradually consumed.

The mark left by the pedicel falling off on the    seed is called the hilum. A tiny hole, the seed hole, can also be seen in the mature seed. The seed coat shows beautiful lines under a high-power microscope. Some cactus seeds also have special structures, such as aril. It is developed from the pedicel of the moon and forms a long protuberance outside the mature seed. Other seeds have spongy or cork-like appendages near the seed hole.

When    seeds germinate, they will swell at first, then the seed coat will crack and the radicle will protrude from it. At this time, it is the most important to ensure water absorption, because the nutrient tissue of the seed can also meet the nutrient needs of the new buds for a period of time. Because most of the cactus seeds sprout close to the surface, green seedlings can quickly begin photosynthesis. We will explain the conditions for sprouting in more detail in the sowing. Many columnar cacti take years to bloom for the first time. As the plant grows, large tree-like or shrubby cactus will produce a lot of corked tissue in the plant. This woody tissue (xylem) is also formed by the cambium.

Finally, a cylinder-shaped protective layer is formed. The xylem of the cactus does not have eye-catching rings, so it is impossible to determine its age. It is speculated that giant tree-shaped cacti, such as the giant cactus, can live up to 250 years. The xylem of cactus is mainly composed of rectangular wooded thick-walled cells. Unlike most xylem, xylem cells are alive and contain starch. The work of transporting water is mainly done by long tubular cells, that is, ducts.

   recommended articles:

Detailed explanation of leaves and roots of    cactus

Formation of Young Stem of    Cactus

External structure and morphology of    cactus

An outline of the evolution of    "living fossil" cactus