Allergic response produce histamines. These histamines will act on different areas of the body (eyes, throat, nose, gastrointestinal tract, skin or lungs) to produce symptoms of an allergic reaction. The allergic response is not limited to a certain amount of exposure. If the body is exposed to the allergen multiple times the immune system will react every time the allergen is present. The reason why people get allergies is not known. The allergens are not passed down through generations. It is believed if parents have allergies the child is more likely to be allergic to the same allergens. Some common symptoms include
Pollen tube tubes. The presence of multiple grains of pollen has been observed to stimulate quicker pollen tube growth in some plants. The vegetative cell then produces the pollen tube, a tubular protrusion from the pollen grain, which carries the sperm cells within its cytoplasm. The sperm cells are the male gametes that will join with the egg cell and the central cell in double fertilization. The germinated pollen tube must then drill its way through the nutrient-rich style and curl to the bottom of the ovary to reach the ovule. Once the pollen tube reaches an ovule, it bursts to deliver