. Principles of modern biology. Biology. The Plant Kingdom - 595 MATRIX _ SHEATHS- CELL OSCILLATORIA ^y\. , A MATRIX SHEATH. GLEOCAPSA NOSTOC Fig. 31-1. Some blue-green algae (Cyanophyta). Note the absence of nuclei and chloroplasts in the primitive cells. None of the blue-greens reproduces sexually. the most ancient and primitive of all green plants. Most of the 2000 or so known species display a bluish-green color, owing to the presence of a blue pigment, phycocyanin, which is mixed with the chlorophyll. How- ever, red and yellow pigments are also found in the cytoplasm, and some of the spec
. Principles of modern biology. Biology. The Plant Kingdom - 595 MATRIX _ SHEATHS- CELL OSCILLATORIA ^y\. , A MATRIX SHEATH. GLEOCAPSA NOSTOC Fig. 31-1. Some blue-green algae (Cyanophyta). Note the absence of nuclei and chloroplasts in the primitive cells. None of the blue-greens reproduces sexually. the most ancient and primitive of all green plants. Most of the 2000 or so known species display a bluish-green color, owing to the presence of a blue pigment, phycocyanin, which is mixed with the chlorophyll. How- ever, red and yellow pigments are also found in the cytoplasm, and some of the species are reddish and a few are brown-green. Many cyanophytes live in fresh waters. In reser- voirs and lakes, they sometimes pollute the water seriously by their great abundance. Also there is a large number of marine spe- cies. Occasionally a red species, prevalent in the Red Sea, flourishes in such numbers that the water actually becomes colored. A few blue-greens live on damp soil, in moist shady spots; or on the damp outer surfaces of flowerpots in humid greenhouses. The primitive status of the blue-green algae is indicated by the fact that none of them is multicellular. Many are of solitary, unicellular habit, but others form colonial aggregates, such as are shown in Figure 31-1. Frequently the cells of the colony are pro- tected by one or more gelatinous coverings of pectinous material. The colonies may be threadlike (filamentous), or they may be more or less ball-like (Fig. 31-1). Another primitive feature of the cyano- phytes is their extremely simple cell struc- ture. Definite nuclei have not been devel- oped in the cells. The granules of nuclear material (chromidia) are not enclosed within a nuclear membrane. They tend to be scattered more or less evenly throughout the cytoplasm (Fig. 31-1). However, in some spe- cies (Fig. 2-3), the chromidial granules may be aggregated toward the center of the cell— a sort of transitional stage in the evolution of true nuclei. More
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