Tree pollens, grass pollens, and weed pollens cause allergic nasal symptoms in millions of people. Pollen is that part of plants that contains the male genetic material. The units in which this material is held are called pollen grains. Two walls surround the genetic material in each grain. The innermost wall, the intine, is very thin and fragile. The outer protective wall, the exine, is relatively thick and highly resistant to destruction. Pollen grains from different plants look as different from one another as do the plants from which they come, a fact which is best appreciated when the grains are stained with special chemicals and viewed under a microscope. This is, in fact, what is done when a pollen count is made. Stained pollen grains are beautiful, intricate structures. For example, ragweed pollen resembles a golf ball, oak pollen an intergalactic star-fighter, and cypress pollen, Рас Man.
Pollination is the term used to describe the transfer of pollen grains from the anther, the male organ of plants, to the stigma, the female organ of plants. Once transfer is completed, fertilization can take place. Surprisingly, only a small percentage of the thousands of plant pollens that exist are released into the air under circumstances sufficient to allow them to cause nasal allergy symptoms.
For a pollen to cause nasal allergies, it must meet four requirements:
- It must be produced in massive quantities.
- Its primary process of pollination must be via wind, not insects.
- It must be able to stimulate our immune system to produce an allergic response.
- We humans must be sufficiently exposed to the pollen to develop an allergy.
In order to be successfully wind pollinated, a plant and its pollen must have the following characteristics:
- A large number of pollen grains must be produced.
- The pollen must be aerodynamically sound, i.e., it must be of the right size, structure, and weight to be carried by the wind.
- The structure of the plant and its geographic location must favor the release of pollen into the wind.
- Pollen release during the season and during the day must be timed to optimize capture by the female organ.
- Like plants should be closely spaced to one another.
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