. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 176 BOTANY the filaments branch ? Are they fastened at one end ? A filament is com- posed of a number of cells placed end to end. Notice a single cell rather carefully with the low power first, and then under the high power. The following structures can be made out by the careful observer: — (a) The cell wall. (b) The chlorophyll bands. Determine if there is one or more in a single cell. The number varies in different species. (c) The colorless protoplasm; this is usually best seen close to
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 176 BOTANY the filaments branch ? Are they fastened at one end ? A filament is com- posed of a number of cells placed end to end. Notice a single cell rather carefully with the low power first, and then under the high power. The following structures can be made out by the careful observer: — (a) The cell wall. (b) The chlorophyll bands. Determine if there is one or more in a single cell. The number varies in different species. (c) The colorless protoplasm; this is usually best seen close to the cell wall. (d) The nucleus, suspended in the middle of the cell by strands of proto- plasm. Draw a single cell as you see it under the high power of the microscope, and label each part mentioned above. Pond scum may grow by a simple division of the cells in a filament. Another method of reproduction is seen in this plant. The cells of two adjoining filaments may push out tubes which meet, thus connecting the cells of two different filaments with each other. Meantime the proto- plasm of the cells thus joined condenses into two tiny spheres; the bands of chlorophyll are broken down, and ultimately the contents of one of the cells passes over tho tube and mingles with the cell of the neighboring filament, with which it was pre- viously connected by the tube formed from the cell walls. As in black mold, the result of this process of fusion is a thick-walled resting cell which we call a zygospore. This cell can withstand con- siderable extremes of heat and cold, and may be dried to such an extent that it is found in dust or C^ in the air. Under favorable conditions, this spore ' ' ' will germinate and produce a filament. Conjugation. — The process in which two cells of equal size unite to form a single cell is called conju- gation. It is believed to be a sexual process which corresponds in a way to the fertilization in the If material is obtainable, draw several stages in.
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