Benefits of cross-pollination, Biology

Benefits of Cross-Pollination

Because of the specific benefits of cross-pollination, flowering plants have evolved many devices to prevent self-pollination and to encourage cross-pollination. The most common ones are described as follow:

i. Dichogamy: In many species the anthers and the stigma come to maturity at different times. That is, the dehiscence of anthers and the receptivity of the stigma of a flower do not coincide. In the sunflower plant, the anther dehisces before the stigma becomes receptive and thus self-pollination cannot occur. This condition is termed as protandry. In Mirabilis, and Magnolia the stigma becomes receptive before the anthers dehisce. This condition is called protogyny.

ii. Herkogamy: Some species show structural adaptations to prevent pollen grains from coming into contact with the stigma of the same flower. In many herkogamy species the relative position of the anthers and the stigma is such that self- pollination cannot occur. For example, the stigma in many plants projects beyond the level of anthers and as a result the pollen of the same flower cannot land on the stigma. Similarly the pollinia (pollen in sacs) of orchids and Calotropis cannot reach the stigma of the same flower.

iii. Self-sterility: In many species, self-pollination does not result in fertilization. This is because pollen germination on the stigma or the growth of pollen tubes in the stigma or style is inhibited. For effective fertilization, pollen has to come from another plant. Self-sterility is widespread in flowering plants. It is estimated that about half the total number of species of flowering plants exhibit this phenomenon. It is genetically controlled and is considered a primitive character. It seems to have evolved very early in the evolution of flowering plants as an effective mechanism for out breeding.

iv. Dicliny: In these species flowers are unisexual. Male and female flowers are borne either on the same plant (e.g., many cucurbits). This condition is referred to as monoecious. When male and female flowers are borne on different plants (e.g., date palm, mulberry, cannabis) the condition is called dioceous. Since pollination in these, including the monoecious plants, involves two different flowers, it is considered as cross-pollination.

Posted Date: 1/23/2013 3:00:57 AM | Location : United States







Related Discussions:- Benefits of cross-pollination, Assignment Help, Ask Question on Benefits of cross-pollination, Get Answer, Expert's Help, Benefits of cross-pollination Discussions

Write discussion on Benefits of cross-pollination
Your posts are moderated
Related Questions
In the RBC, glucose can be oxidized to two primary products. One of the oxidation proucts is ribulose 5 phosphate, and the other is which of the following compounds? -lactate

What are the typical vegetation and the typical fauna of the temperate forests? In the temperate forest deciduous trees predominate. Various Mammals are found in great number,

Q. Why is AIDS difficult to prevent by vaccination? It is not easy to produce a vaccine against AIDS because the HIV is a highly mutant virus. In approximately every replicatio

Q. What is Revisions? Revision accounts for only a section of a genus or for the elements as restricted to a continent or smaller geographical area. Some revisions are based so

Explain the Numerical Taxonomy? Numerical methods in taxonomy are not new. Simple statistical methods like standard deviations, t-tests and chi-squared have been used for sever

Discuss in detail about the Close Head Injuries Closed-head injuries result from a blow to the head, which can subject the brain to a variety of mechanical forces: Damag

Explain the periodic table of the elements ? Periodic Table of the Elements :  An element is a pure substance composed of atoms all of a single kind. It cannot be broken down

VASCULA R TISSUES (= FLUID TISSUES) - The vascular tissues are of two types: blood and lymph.

The protocol includes four treatment modalities: A = Mechanical Debridement In this the patients are re-instructed in oral hygiene and motivated to initiate and continue m

What do protozoans "eat"? Do they move in search for food? Protozoans are heterotroph beings, i.e., they do not make their own food and therefore they require to search for it