OSCILLATORIA. 27 



analogies with the cuticle of the higher plants. The chlo- 

 rophyll is evenly distributed throughout the protoplasm. 

 The study of the protoplasm and chlorophyll is much 

 obscured by the presence of the peculiar coloring-matter, 

 phycocyanin, characteristic of all the Cyanophyceae. 

 Phycocyanin is insoluble in alcohol, but soluble in water 

 when the plants are dead; while chlorophyll is soluble 

 in alcohol, but not in water; hence from dead plants 

 water removes the phycocyanin, and alcohol the 

 chlorophyll. This blue color is often seen on the sides 

 of vessels in which Oscillatoria has remained so long as 

 to die, and also staining the herbarium sheets on which 

 specimens have been dried. 



The cells are kept together chiefly by the investing 

 sheath, into which they are packed. This structure, 

 together with the community of action exhibited in pro- 

 ducing the peculiar oscillating and nutating movements, 

 makes it evident that the cells of each filament have a 

 certain dependence upon one another, although at the 

 same time each is capable of independent existence. 

 It may be that the smallness of the cells and the thinness 

 of their walls is in some way correlated with this unity 

 of function. It is not yet definitely known how the 

 movements in Oscillatoria are produced. 



Turgidity is a characteristic of living cells. It is 

 the chief means by which the soft parts of plants are 

 enabled to keep their form, and otherwise to act normally. 

 It is brought about by the ability of the protoplasm to 

 keep certain substances from escaping through it, while 

 their presence causes water to pass in until a considerable 

 internal pressure is created. 



