. Botany for agricultural students. Plants. SPIROGYRA 315 abundant fresh water plants, and in the examination of other forms of fresh water Algae with the microscope one usually finds some Desmids present. The cell is peculiar in being organized into symmetrical halves, which are separated by a constriction that forms an isthmus. The nucleus is in the isthmus, and in each half there is a chloroplast and a number of pyrenoids. They reproduce in two ways, by cell division and by zygo- spores. In multiplying by cell division, the cell divides at the isthmus, the halves separate, and the portion o
. Botany for agricultural students. Plants. SPIROGYRA 315 abundant fresh water plants, and in the examination of other forms of fresh water Algae with the microscope one usually finds some Desmids present. The cell is peculiar in being organized into symmetrical halves, which are separated by a constriction that forms an isthmus. The nucleus is in the isthmus, and in each half there is a chloroplast and a number of pyrenoids. They reproduce in two ways, by cell division and by zygo- spores. In multiplying by cell division, the cell divides at the isthmus, the halves separate, and the portion of the isthmus re- maining to each half develops a new half and thus a new individ- ual is formed. In sexual repro- duction the cells pair and the protoplasts, which escape through ruptures at the isthmus, fuse and form a zygospore. Sometimes the cells after pairing become con- nected by a tube through which the protoplasts reach each other. In either case the entire proto- plasts of cells conjugate. Spirogyra, — Spirogyra {Fig. 271), very common in ponds, sluggish streams, and watering troughs, is the most familiar fila- mentous form of the Conjugales and the one most commonly studied in elementary classes. It gets its name from its large and beautiful spiral chloroplasts. Its cells are all alike and it pro- duces no zoospores. Its sexual reproduction, in which the gam- etes reach each other through tubes, is its important feature. Under certain conditions, filaments pair and line up side by side. In this position, the cells of the filaments grow toward each other in tubular projections which unite and form open passage ways between the cells of the paired filaments. The protoplasts of one filament pass through these tubes and fuse with the pro-. A Fig. 271. — A species of Spiro- gyra. A, a portion of a filament showing a vegetative cell with its spiral chloroplasts (c) and nucleus (/() (X 100); B, filaments conju- gating and two zygospores (z) fully formed; C, a zygospore
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectplants, bookyear1919
