Main Difference – Self vs Cross Pollination
Self and cross pollination are the two methods of pollination in plants during their sexual reproduction. During self pollination, polling grains are transferred from an anther of a flower either into the stigma of the same flower or a different flower of the same plant. In contrast, pollen grains are transferred from the anther of a flower into a different flower of a different plant of the same species during cross pollination. The main difference between self and cross pollination is the nature of the offspring; pure line progeny can be obtained by self pollination whereas offspring with genetic variations can be obtained by cross pollination.
This article looks at,
1. What is Self Pollination
– Characteristics, Mechanism, Offsprings
2. What is Cross Pollination
– Characteristics, Mechanism, Offsprings
3. What is the difference between Self and Cross Pollination 
What is Self Pollination
The deposition of pollen grains from the anther of a flower on the stigma of the same flower or on the stigma of a different flower in the same plant is called self pollination. Self pollination occurs between anthers and stigma of genetically identical flowers, producing genetically identical offspring to parents. Several types of reproduction methods are observed in self pollinating plants. The pollination within the same flower is called autogamy. In some plants, several flowers are connected to the same stem. In these flowers, pollen grains of the different flowers pollinate flowers in the same stem. This is called geitonogamy. The carpels and stamens are of the same length, grouped together in flowers, which use geitonogamy. Some flowers are self pollinated even before the opening. This is called cleistogamy. Some of the plants which exhibit cleistogamy are never opened. The advantage of self pollination is that plants are capable of reproducing while even there are no external pollinating agents to assist the pollination. The disadvantage of self pollination is that it reduces the genetic diversity of plants in the same species.
Figure 1: Self Pollination
What is Cross Pollination
The deposition of pollen grains of the anther of one flower on the stigma of a flower of a different plant of the same species is called cross pollination. The type of reproduction which is used in cross pollination is allogamy. The genetic material of two plants is combined during cross pollination, producing a genetically varied offspring of the parents. Better tomato variants are produced intentionally by cross pollination. Cross pollination requires external pollinating agents like water, wind, animals and insects. Animals like birds and insects like ants, butterflies, beetles and bees are involved in the cross pollination. The most common pollinators are honey bees. Cross pollinating flowers consist of several characteristics like brightly-colored petals, nectar and scent in order to attract insects as well as long stamens and pistils in order to shed pollen grains onto the body of insects and achieve pollen grains from different plants, which are carried out by insects. Those cross pollinating flowers consist of several mechanisms like the maturation of stamens and carpels in different times in order to prevent self pollination as well. A bee is pollinating a rose is shown in figure 2.
Figure 2: Cross pollination
Difference Between Self and Cross Pollination
Mechanism
Self Pollination: During self pollination, pollen grains are transferred from an anther of a flower either into the stigma of the same flower or different flower in the same plant.
Cross Pollination: During cross pollination, pollen grains are transferred from the anther of a flower into a different flower of a different plant in the same species.
Number of Plants involved in Pollination
Self Pollination: A single plant is involved in the self pollination.
Cross Pollination: Two different plants of the same species are involved in the cross pollination.
Occurrence
Self Pollination: Self pollination occurs between genetically identical flowers.
Cross Pollination: Cross pollination occurs between genetically different plants of the same species.
Perfect/Imperfect Flowers
Self Pollination: Self pollination occurs only in perfect flowers.
Cross Pollination: Cross pollination can occur in both perfect and imperfect flowers.
Differences in Plants
Self Pollination: Plants which use self pollination contain small flowers.
Cross Pollination: Cross pollinating flowers typically have brightly-colored petals, nectar and scent as well as long stamens and pistils.
Successfulness of the Method
Self Pollination: Self pollination is a sure method, which rarely fails.
Cross Pollination: Cross pollination can sometimes fail.
External Pollination Agents
Self Pollination: External pollination agents are not necessarily required for self pollination.
Cross Pollination: External pollination agents are necessarily required by cross pollination.
Pollination Methods
Self Pollination: Shed pollen directly fall on the stigma.
Cross Pollination: External pollination agents like wind, water, animals and insects like bees are required for the transferring of pollen grains.
Number of Pollen Grains
Self Pollination: Self pollinating flowers produce a small number of pollen grains.
Cross Pollination: Cross pollinating flowers produce a large number of pollen grains.
Reproduction Types
Self Pollination: Autogamy and geitonogamy are the types of reproduction in cross pollinating plants.
Cross Pollination: Allogamy is the type of reproduction in self pollinating plants.
Offsprings
Self Pollination: Homozygous offspring is resulted by self pollination.
Cross Pollination: Heteroygous offspring is resulted by cross pollination.
Genetic Variations in the Offspring
Self Pollination: Pure line progeny can be obtained by self pollination.
Cross Pollination: Genetic variations can be observed in the cross pollinated offspring.
Contribution to Evolution
Self Pollination: Self pollination has no contribution to evolution.
Cross Pollination: Cross pollination is involved in the evolution.
Characters
Self Pollination: Undesirable characters cannot be eliminated, but desirable characters can be concentrated by self pollination.
Cross Pollination: Undesirable characters can be eliminated as well as the desirable characters.
Examples
Self Pollination: Self pollination is seen in peanuts. orchids, peas, sunflowers, wheat, barley, oats, rice, tomatoes, potatoes, apricots and peaches.
Cross Pollination: Flowers of apples, grapes, plums, pears, raspberries, blackberries, strawberries, runner beans, pumpkins, daffodils, tulips, lavender are cross pollinated by insects. Flowers of grasses, catkins, dandelions, maple trees, and goat’s beard are cross pollinated by the wind.
Conclusion
Self pollination and cross pollination are the two types of mechanisms, which are used by plants during their sexual reproduction. Self pollination is the deposition of pollen grains of one flower on a stigma of a second flower, which is genetically identical to the first flower. Self pollination does not produce genetically varied offspring. Hence, it has no contribution to evolution. But, preferred traits can be conserved through the progeny by self pollination. The deposition of pollen grains of one flower on the stigma of another flower of the same species, which is genetically varied to the first flower is cross pollination. Cross pollinating flowers exhibit special characteristics in order to attract external pollinating agents like animals and insects to the flower. These characteristics are bright color, large petals, nectar and scents. Genetically varied offspring can be obtained by cross pollination, achieving beneficial traits. However, the main difference between self and cross pollination is in their contribution to evolution.
Reference:
1. Gilbert, Scott F. “Pollination.” Developmental Biology. 6th edition. U.S. National Library of Medicine, 01 Jan. 1970. Web. 23 Apr. 2017.
2. “Self Pollination.” BuzzAboutBees.net. N.p., n.d. Web. 23 Apr. 2017.
3. Rhoades, Heather. “What Is Cross Pollination – Learn About Cross Pollination In Vegetable Gardens.” Gardening Know How. N.p., 01 May 2016. Web. 23 Apr. 201
Image Courtesy:
1. “Self-pollination(1)” By Jankula00 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Bee pollinating a rose” By Debivort – Own work (CC BY-SA 3.0) via Commons Wikimedia
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