783 



reaction was noticed (positive geotaxis), whereas in the literature 

 Chlamydomonas pulvisculus is stated to fiave a negative geotactic 

 reaction. Very dilute acids and phosphates were found to be positive 

 chemotactics for Chlamydomonas. The alga reacted with negative 

 geotaxis to more concentrated acid solutions and to bases. 



All these reactions were clearly observed with the alga in 

 distilled watei-. Addition of small quaniilies of acid and base caused 

 the reactivity to decrease. Above a certain concentration no reaction 

 occurred. It could be observed microscopically that in such cases the 

 motility was greatly diminished. The i-eactivily and motility could 

 also be decreased by adding salts. The concentrations for salts were 

 greater than for acids .and bases, but nevertheless still small. 



Increase of electrolyte concentration (whether by addition of acid, 

 base, salts or combinations of these) diminished the sensitiveness to 

 light, to gravity and to chemotactics to an approximately equal 

 extent. By means of the reactions indicated the influence of electro- 

 lytes on the motility of the alga was investigated. 



It was very easy to separate the individuals of Chlamydomonas 

 from the culture-fluid. For this purpose the fact was utilized that 

 in cultures sufïiciently dense for experiments, the alga was in such 

 a condition that it readily attached itself to solid bodies. A glass 

 tube of about 0.5 cm. diameter, sealed at its lower end more or 

 less to a point, was filled with the culture fluid. The tube was placed 

 vertically in unilateral diffuse daylight. After five minutes a green 

 band of algae was visible at one side of the tube. In this condition 

 the motility is still so great that the algae all swim to one side of 

 the tube, where they come info contact with its wall. Inconsequence 

 of this contact they had fastened themselves to the glass. They were 

 so firmly attached that it was possible to suck out the culture fluid 

 with a pipette while the algae remained sticking to the wall. Next 

 a quantity of distilled water was introduced into the tube, which 

 was then shaken to distribute the algae in the water. The tube was 

 again placed in a vertical position and exposed to unilateral diffuse 

 daylight. Under the influence of the distilled water the algae showed 

 not the slightest tendency to attach themselves. The light indeed 

 caused them to collect on one side of the tube as a dense green 

 band, but under the influence of gravity the algae constituting this 

 band soon moved to the bottom, so that after five minutes there 

 was a distinct accumulation at the lower end. 



By means of a pipette the water could now be removed almost 

 completely. After this preparation of the algae the solution of which 

 the eff"ect was to be investigated, was introduced into the tube. 



51* 



