Cytology and Movements of the Cyanophycece . 311 



by alternate shortening and stretching of the opposite halves 

 of the cells, and depending partly on the living energy of the 

 cells and partly on the ductility and elasticity of their mem- 

 branes." In another place (17) he carried out the same 

 idea of expansion and contraction as follows : "Flexible 

 Oscillaria filaments are capable of bending themselves spon- 

 taneously and of stretching themselves either straight out 

 or curving themselves into snake-like forms, or entwining 

 around other filaments." He could faintly make out a 

 delicate protoplasmic pellicle covering the whole trichome. 

 The unequal contraction of this pellicle assisted to cause 

 the unequal contractions noted. 



Hansgirg (35) concluded that motion was due to heat 

 and light. The creeping movements took place within a 

 very thin gelatinous sheath which fastened itself to some 

 substratum and the organism moved backwards and for- 

 wards in this, leaving it extended behind the organism in a 

 reed-like tube. This substantiated the observations of 

 Schultze (70), though he considered the reed-like tube to 

 be visible only on the sharpest inspection. This surrounding 

 layer of slime was considered to be the same as that which 

 Engelmann (22) described as a surrounding protoplasmic 

 layer, though on account of its dififerent stainability with 

 iodine, Hansgirg concluded that it was not protoplasmic. 

 Further, if the organism was cultivated in darkness, this 

 sheath of slime disappeared and the organism lost its 

 motility. He thought the force, which caused the various 

 movements of Oscillaria, was generated by osmotic currents 

 passing into the protoplasm of the filament. "For," he 

 continued, "I have established by definite observations that 

 a powerful strength of imbibition is peculiar to the pro- 

 toplasmic content of the cells of this organism, and this 

 strength of imbibition works as long as the cell lives." 

 And again he said : "According to my view, the move- 

 ments of those Oscillaria filaments which are enclosed 

 in an osmotic sheath in which they move backward and 



