10 



PLANT MORPHOLOGY 



Although ciUa are never present, many of the filamentous blue-green 

 algae have the power of movement. If a mass of Oscillatoria growing 

 on mud is placed in a flat dish, the filaments soon creep out in all direc- 

 tions. Under the microscope the filaments are seen to shift frequently 

 their position laterally in the water. In performing these movements, 

 the cause of which is unknown, the cells of the colony function as a unit, 

 thus approaching a condition characteristic of multicellular plants — a 

 cooperation of cells in the performance of their functions. 



Fig. 2. Longitudinal sections through cells of Anabaena circinalis, some of which are 

 dividing, X 2,750. The nuclear material is in the form of irregular masses. The spherical 

 bodies are cyanophycin granules and represent reserve food. {After Haupt.) 



Cell Structure. The Cyanophyceae are characterized by a very primi- 

 tive cell structure. A thin cell wall, composed of cellulose and pectic 

 compounds, seems always to be present. Generally it becomes mucilag- 

 inous and forms a matrix around the cell. The protoplast lacks the 

 degree of organization seen in the higher plants. It consists of an outer 

 colored portion, containing the blue and green pigments, and a central 

 colorless portion. The latter, representing an incipient nucleus, con- 

 tains a mass of scattered chromatin granules not surrounded by a mem- 

 brane and without a nucleolus (Fig. 2). Plastids are not organized, the 

 pigments being merely diffused throughout the peripheral region of the 

 cell. Carbohydrate food is stored as glycogen, starch being absent. 

 Reserve food often occurs also as minute oil droplets and as spherical 

 bodies (cyanophycin granules) that are probably protein in nature. 



