Page:The New International Encyclopædia 1st ed. v. 01.djvu/650

ANGIOSPERMS. "loiip they are flat and open, exposing the ovules, and giving rise to the name, which means "seeds naked." In order to understand the following state- ment of the technical eharaoters of angiosperms, it will be' necessary to read the articles Alterna- tion OF Genek.ti'ons, and Heterospoky.

In its germination the pollen grain (micro- A ma'ure embrvo-sac (c). showing the three antipodal cells («i, the two polar nuclei fusing to form the endosperm nucleus (/)i, the two synergids (s), the egg (o), and the jiollen- tube entering to discharge its sperm cells. The two integu- ments (!) of the ovule are also shown. spore) produces within itself usually three cells, which represent a very much reduced male plant. One of these cells later develops the pollen tube, which penetrates to the egg, while ciated with it are two other cells called syner- r-ids (helpers). This group of three cells is called the egg apparatus. At the opposite end of the sac is a group of sterile cells, usually three in number, and called the antipodal cells. More centrally placed in the sac is the seventh cell, that lias been formed by the fusing of two cells, and, after the fertilization of the egg, is to de- velop the endosperm (nutritive tissue of the seed) . This cell is called the "definitive nucleus" or "primary endosperm nucleus." Before fer- tilization, the pollen grain containing the male plant is transferred by the wind or by insects to the stigma (receptive region of the pistil), the process of transfer being called pollination (q.v.). After pollination the pollen tube is de- veloped, which penetrates the pistil and finally reaches the ovule, carrying in its tip the two male cells or sperms, the tip of the tube then enters the micropyle, crowds its way to the egg, and discharges its' contents. One sperm passes to the egg and fuses with it, this act being called fertilization. The other sperm has recently been observed to pass on in the sac and fuse with the endosperm nucleus; but it remains to be seen how general this phenomenon, called double fer- tilization, may be in the group.

ANGLAISE, iiN'glaz'. An English country dance {coutiedansc), in 2-4, 3-4, or 3-8 time. It is gay, and probably originated in the older form of the French ric/audnn. See.

AN'GLE (Lat. angulus, a corner, GIv. ayKv'/.oc:, aiilijlos. bent). One of the common geometric concepts. If two lines meet, they are said to form v.n angle, the lines being called the arms, sides, or legs, and the point of meeting the vertex of the angle. The size of the angle is determined by the amount of turning necessary to carry a moving radius from one arm to "the other," and hence is independent of the length of the arms.

If the arms of an angle are in the same straight line on opjjosite sides of the vertex, a

An embryo sac (e), showing the young embryo (w), endosperm cells (zy, and the three disorganizing antipodal cells (a).

the other two cells are the sperms. The embryo sac within the ovule, which represents a single unshed spore, produces within itself a group of cells, usually seven in number, which represent a reduced female plant. In the end of the sac toward the micropyle {the opening left by in- tegument) the single egg is situated, and asso- straight angle (fig. I) is formed; half of a straight angle is called a right angle (fig. 2); two straight angles equal a perigon or angle of 3(i° (fig. 3). Angles are also conceived exceed- ing 3(i0°; tluis an angle of 720° is described when a screw is turned twice around. An angle between 0° and 00° is said to be acute (fig. 4); one between 90° and 180°. obtuse (fig. 5); one between 180° and 3(30°. reflex (fig. 6). An- gles are considered as positive if generated by a radius moving counter-clockwise, and negative