Plants causing allergies: grasses and weedsCharacteristics of the Grasses That Cause Allergy Grasses cause three times as many allergies as trees because they grow almost anywhere in the world (from the frozen North to the equator), even though they thrive best in moderate climates. There are many kinds of grasses, some of which, like sugar cane, wheat, rye, corn, bamboo, and rice, are planted so far from human habitations that they rarely cause allergies. Timothy, Johnson orchard, Bermuda, blue, and June are the names of grasses which can cause allergies. They grow in meadows and lawns in and around densely populated areas and pollinate in the United States from May to August. Allergy to grasses is easily diagnosed because the pollen of all grasses looks the same when seen under a microscope; as a result, the pollen of any kind of grass can be used for testing or desensitization. (There are two exceptions to this rule: Bermuda and Johnson grasses, which have importance only in limited localities.) In subtropical countries like Israel, grasses pollinate all year around and are the main cause of pollen allergy. Characteristics of the Weeds That Cause Allergies The most common cause of pollen allergy in the United States is weeds. Some weeds, like English plantain, pollinate in June and July, while ragweed pollinates from the middle of August to the first frost. There is a short variety of ragweed, a tall variety, and a giant one. The short variety reaches a height of one to five feet and has hairy green stems, parted leaves, and long green-to-yellow spikes. The giant variety may reach a height of fifteen feet and has either three-lobed or simple leaves. Both plants can live in the poorest of soils and can resist all severe weather conditions but snow. About mid-August, a photochemical reaction (which depends upon the balance between daylight and darkness) causes all ragweed plants to produce flower spikes which contain pollen. After a day or two, pressure builds up in the spikes, they burst open, and the pollen is thrown out into the air. It lands on the plant's leaves, dries up, and is then carried away by the wind for hundreds of miles. All ragweed pollen looks and acts very much alike, no matter what variety of ragweed plant originated it. *17/99/5* ALLERGIES «Canada Online Pharmacy» |
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