26 ALGJE 



Histology. The individual plants are composed of two 

 types of cells arranged in a filament or chain covered with 

 mucilage. This enables them to withstand drought and to 

 live on land. Most of the cells forming the chain are nearly 

 circular, the wall is colorless and the protoplasm does not 

 appear to be differentiated into plastids and nuclei. The 

 blue-green color is due to phycocyanin, a bluish pigment, 

 and to chlorophyll. Among these cells occur at regular inter- 

 vals heterocysts, which are colorless cells without protoplasm. 



Reproduction. Nostoc reproduces asexually, first by simple 

 fission or the equal division of its cells to form two cells; 

 secondly by fragmentation or the breaking up of the filaments 

 into sections, the section in each case being the part of the 

 filament between the heterocysts. The sections finally work 

 their way out of the mass of jelly and by repeated cell division 

 start a new colony. 



Conclusion. Nostoc consists of a colony of one-celled 

 plants, each independent of the other but arranged in the 

 form of a filament or chain. The mucilage secreted by the 

 wall enables the plant to form colonies. Reproduction is 

 asexual by simple fission and fragmentation. 



BLADDER WRACK (Fucus Vesiculosus) 



Habitat. Fucus is a seaweed found in great quantities 

 along rocky shores, where at low tide thousands of plants 

 may be seen growing on the rocks. 



Morphology. The plant body or thallus is firmly attached 

 to a rock by a flat disk-like part called a holdfast. Above 

 the holdfast the thallus is cylindric. Next to this cylindric 

 part is the flat leaf-like part of the thallus with a thicker 

 central region. At frequent intervals the thallus is enlarged 

 to form air cavities or vesicles which are filled with mucilage 



