Archimedes reportedly came upon this discovery in his bathtub, and ran out into the street without his clothing shouting "Eureka, I have found it. The principles of buoyancy and specific gravity are utilized in many ways, from scuba diving and chemistry to the hardness of dry, seasoned wood.
Some of the heaviest hardwood trees and shrubs of the United States have specific gravities between 0. Although some of these trees are called ironwoods, their dense, dry wood will still float in water. Since the pure cell wall material lignin and cellulose of wood has a density of about 1. True ironwoods include trees and shrubs with dry, seasoned woods that actually sink in water, with specific gravities greater than 1.
They include lignum vitae Guaicum officinale , 1. To appreciate the weight of these hardwoods, compare them with tropical American balsa Ochroma pyramidale , one of the softest and lightest woods with a specific gravity of only 0. Fuzzy brown cattail spikes Typha latifolia contain dense masses of tiny seeds, each with a tuft of silky hairs.
Each spike contains about a million seeds. They are shed by the millions in a cloud of white fluff. Tumbleweeds are pushed along by the wind, scattering thousands of seeds as they roll across open fields and valleys.
A tumbleweed of this size is difficult to hold on to during a strong wind storm. A tumbleweed "snowman" in San Diego County made from three dried plants of Salsola tragus. Squirrel-Tail Grass Elymus elymoides , formerly named Sitanion hystrix is an attractive grass native to the mountains and plains of the western United States.
Seed-bearing sections spikelets of the flower spike containing one-seeded fruits called grains and very long awns are carried short distances by the wind. Although not as efficient fliers, the long awns function like the parachute bristles pappus of composites. Wind Dispersal References Jones, K. Healing Arts Press, Rochester, Vermont. Loewer, P. Macmillan Company, New York. Seeds contained within fruits need to be dispersed far from the mother plant so that they may find favorable and less-competitive conditions in which to germinate and grow.
Some fruits have built-in mechanisms that allow them to disperse by themselves, whereas others require the help of agents such as wind, water, and animals. Modifications in seed structure, composition, and size aid in dispersal. Wind-dispersed fruit are lightweight and may have wing-like appendages that allow them to be carried by the wind. Some have a parachute-like structure to keep them afloat.
Some fruits, such as the dandelion, have hairy, weightless structures that are suited to dispersal by wind. Seeds dispersed by water are contained in light and buoyant fruit, giving them the ability to float. Coconuts are well known for their ability to float on water to reach land where they can germinate. They spin like helicopters as they fall from the tree, providing a longer time for dispersal by wind. Halesia carolina Carolina silverbell - four angled fruits have wings at each corner.
Liriodendron tulipifera tulip-tree - The flowers bloom high in the tree. As each winged fruit peels off the outside, it flutters to the ground. Ulmus americana American elm - The wings of the one-seeded samaras form partly from the persistent and enlarged styles. Carduus nutans nodding plumeless thistle - The dry, one-seeded fruits are carried on the wind by plumose "parachutes". Typha latifolia broadleaf cattail - The brown "head" of a cattail is composed of dense, radially arranged "parachutes".
Oranges hold their multiple seeds in the center of the fruit flesh. As oranges ripen on the tree some fruit is dropped, lost to rot, or knocked down by weather. In addition, very bountiful harvests are often more than an owner can pick and consume and excess oranges will invariably fall to the ground when overripe.
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