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CYCADS

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CYPRESS

the simplest of algae, the body consisting of single cells or chains and filaments of cells, and are found in fresh water and damp places everywhere. All the forms show a tendency to become imbedded in a jelly-like substance which is merely the material of their walls transformed into mucilage. In addition to the chlorophyll they contain a blue pigment, which gives the bluish hue to their bodies. Many of them exhibit the power of motion, the free filaments of oscil-laria moving almost continually, while the chains of nos-toc at times wriggle out of the mass of mucilage in which they are imbedded. They have no sexual reproduction, multiplying almost exclusively by ordinary cell-division. In many of their characters, they closely resemble the bacteria, and by many botanists they are associated with them in a common group.

Cy'cads. A group of plants which next to the conifers is the most prominent group of living gymnosperms. They are confined to the tropics and subtropics, and contain about 80 species, nearly equally distributed between the oriental and occidental tropics. The principal genus in the orient is Cycas, and in the Occident Zamia, the latter genus being represented in southern Florida. The stem does not branch, and in many cases rises in a straight column, as in the palm, bearing at its summit a rosette of very large fern-like leaves. In other cases the stem is like a great tuber ensheathed by the thick bases of fallen leaves, and crowned with the rosette of huge fern-like leaves. The seeds are born in cones or strobiles, often of great size, but instead of ripening dry with a hard coat, as in the conifers, they become fleshy on the outside, with a hard stone within, and are much like plums. The group is very fern-like, and probably has come from the ferns. One of the most recent and important discoveries in connection with the group is that their sperms are ciliated and can swim, as in the ferns. See GYMNOSPERMS.

Cy'clone, a phenomenon of the earth's atmosphere, which is practically always exhibited in any region of low barometer, that is, in any region where the pressure of the air has fallen considerably below its average. To understand the nature of a cyclone the student must bear in mind the fact that wind consists simply in the transport of air from regions of high pressure to regions of low pressure. In the northern hemisphere the air does not rush directly in toward the center of a region of low

pressure, but sweeps around toward the center in more or less of a spiral, so that an observer, looking down upon a center of low pressure, would find the wind traveling in a direction opposite that of the hands of a watch. This vorticose motion of the wind is called a cyclone. These cyclones are generally many hundreds of miles in diameter. Now and then they become very small in diameter, and in these circumstances they are apt to be exceedingly destructive, and are called tornadoes. In America these cyclones travel with a speed ranging from 20 to 40 miles per hour. If now we consider a region of high pressure, it is evident that the wind must in general blow away from the center of this region. These winds also assume somewhat of a spiral form, as they do in the case of low-pressure areas: only here the direction of rotation is clockwise. This phenomenon is known as an anticyclone. In general the anticyclone is not marked with the same regularity of structure as the cyclone. In the southern hemisphere the direction of rotation of these two kinds of vortices is exactly the opposite of that found in the northern hemisphere.

Cym'bals are a pair of thin, round, metal plates, with a hollow part in the center, in which a leather strap is fastened for holding the hand. When struck one against the other, a loud, harsh sound is made. They were used in ancient times, by the Greeks, in the worship of the goddess Cybele. The best cymbals are made in Turkey and China. Attempts to discover the composition of the metal have failed. The cymbals generally play the same part as the bass-drum, and in orchestras they are played by the same performer, one cymbal being fixed on the drum, the other held in one hand, while the other hand wields the drumstick. Cymbals are mostly used in military music.

Cyme (sim). A flat-topped cluster of flowers in which the inner flowers bloom first. See INFLORESCENCE.

Cy'press. Species of several genera of conifers. Cham&cyparis contains five species native to North America and Japan. They are all handsome trees, with the opposite scale-like leaves densely clothing the branches. The best-known species are the white cedar of the eastern United States, a tree 70 to 80 feet high; the yellow cedar of the northwest coast, a tree which reaches 120 feet in height; and Lawson's spruce of the Pacific coast, a magnificent tree which sometimes becomes over 200 feet high. Cupressus is a genus containing about ten species, found both in North America and the orient. They resemble the species of Chamcecyparis and are very ornamental evergreen trees, but are hardy only in California and the gulf-states. Taxodmm contains three species, one in China, one

NOSTOC, ONE OF THE CYANOPHYCE^E