How Do Plants Reproduce
Reproduction of Corn
Most corn plants have a single stem, called a stalk, which grows vertically upward from the ground (Figure 2a). The height of the stalk depends both on the variety of the corn and the environment in which a corn plant is grown. As the stalk grows, leaves emerge. A typical corn plant grown by a farmer in the central United States will have a stalk that is 7 to 10 feet tall and has 16 to 22 leaves. The lower part of each leaf wraps around the stalk and is attached to the stalk at a juncture called a node. Typically the lowest four nodes are below ground. Roots develop from each of these nodes. Sometimes, roots develop from the first above ground node, and these are known as brace roots (Figure 2b). Some varieties of corn in certain environments produce secondary stalks, known as tillers, which grow outward from near the base of the main stalk.
Fig. 2a: The primary parts of a mature corn plant. (University of Nebraska-Lincoln, 2005)
|
 Fig. 2b: The primary parts of mature corn roots. (University of Nebraska-Lincoln, 2005) |
Every corn plant has both male and female parts. The male part, which is known as the tassel, emerges from the top of the plant after all the leaves have emerged. The tassel usually consists of several branches, along which many small male flowers are situated. Each male flower releases a large number of pollen grains, each of which contains the male sex cell.
The female floral organ is called an ear. The ear develops at the tip of a shank, which is a small, stalk-like structure that grows out from a leaf node located approximately midway between the ground and the tassel (Figure 3). Occasionally, a plant will produce an ear at several consecutive nodes, but the one that is located uppermost on the stalk becomes the largest ear. The immature ear consists of a cob, eggs that develop into kernels after pollination, and silks. The cob is a cylindrical structure upon which kernel development occurs. The kernels are arranged on the cob in pairs of rows. From each egg, a hair-like structure called a silk grows and eventually emerges from the tip of the husk, which is a group of leaves attached to the shank that encloses the entire ear. Pollination occurs when pollen falls on the exposed silks. Following pollination, a male sex cell grows down each silk to a single egg and fertilization (the union of the male and female sex cells) occurs. The fertilized egg develops into a kernel and inside each kernel is a single embryo (a new plant). A vigorous corn plant may have 500 to 1000 kernels on a single ear.
Fig. 3: An ear of corn with shank and husk. (University of Nebraska-Lincoln, 2005)
Reproduction of Tomatoes
Cherry tomatoes growing in a cluster on the vine. Fertilization is an important and exciting event in the life of the tomato plant. Many processes are involved in this beautiful event. To learn more about these processes scroll downward. The text corresponds to the adjacent picture. |
|
Fertilization takes place in the reproductive organs of the flower. The female organs,comprised of stigma, style, and ovary, collectively are called the pistil. The male organs consist of the anther and filament and are collectively called the stamen. |
|
The tomato flowers of most commercial cultivars are self pollenating (Ho and Hewitt 1986). The pollen from the anther is transferred to the stigma of the same flower. Tomato flowers will be cross pollenated occasionally. When this occurs the pollenator is usually the bumble bee (Hayward 1938). |
|
Once the pollen grain has landed on the stigma the tube cell of the pollen grain elongates to form a tube. This tube reaches down the style all the way to one of the ovules in the ovary of the flower. Once the tube is formed the pollen grain’s two sperm cells then travel down the tube into the embryo sac inside the ovule.(Campbell,1993) |
|
 The ovule is fertilized through a process called double fertilization. It produces a diploid zygote and a triploid endosperm. The endosperm will store food for the embryo.(Campbell, 1993) The fertilized ovule will become one of the seeds of the tomato fruit. The seed contains the embryo and the endosperm and is covered by a strong seed coat, called the testa. The testa is unique to tomatoes. The seed forms a thick outer epidermal layer. These cells partially break down; the “hairs” are what is left behind. These “hairs” collect a gelatinous material which gives the seeds a gooey membrane. This process forms the testa(Hayward 1938). The parts of the embryo are as follows: the shoot apex, two cotyledons (tomato is dicot), the hypocotyl and the root apex.(Ho, Hewitt, 1986) |
|
 Tomato embryo
|
|
Reproduction of Cannabis
Cannabis is a dioecious plant. This means that the plants are either male or female and sometimes even hermaphroditic. Female and male cannabis plants can be identified by their appearance. Female plants are small and bushy and their flowers have pistils. Male plants are long and open, their flowers have stamens.
Male Cannabis Plants
an adult male cannabis plant will produce flowers that grow just about everywhere and form clusters at the bottom. At the right time the male plant opens its flowers and releases very light pollen. This pollen pollinates female plants, but first attaches to the pistils. During growth a male cannabis plant can hardly be distinguished from females. Usually the male plant achieves sexual maturity much earlier than females.
Female Cannabis Plant
the adult female plant produces flower clusters that are an accumulation of chalices and pistils. Each chalice contains an ovule that is fertilized by pollen. When the male plant releases the pollen grains, they attach to long pistils, from where they descend and enter the chalice. In the chalice seeds develop after they have been pollinated. The seed is the product of two different individuals and has the genetic characteristics of both parents. Provided both parents are pure strains or stabilized crossing, the plant will inherit half of each parent.
Hermaphrodite
Sometimes cannabis plants are hermaphrodites. This means they contain both male and female genitalia. These plants can pollinate themselves and can be hermaphrodites in different degrees:
- A majority of female flowers, hard to notice (save)
- Equal number of male and female flowers (discard)
- A majority of male flowers (discard)
Some growers keep the light female hermaphrodite plants to collect the pollen. This pollen is the male part of the reproduction, but is nonetheless genetically female and produces seeds that produce virtually 100% female plants. It is suspected that developing into hermaphrodite plants is connected with the amount of stress the cannabis plant undergoes. But there are varieties that are natural.
References