016 TRANSACTIONS OF SECTION K. 



6. A'otes on the Life History of Hfematococcus lacustris. 

 By M. Wilson, B.Sc. 



This uuicellular alga is characterised by the possession of hsematochrom in 

 various amounts, as well as the ordinary chlorophyll of the cell. While the 

 motile cells are often largely green, the immotile resting cells are red, and these 

 alone can withstand drying. A culture of resting cells in 0-1 per cent. Knop's solu- 

 tion gave motile cells partly green and partly red, and eventually entirely green 

 motile cells. This culture was killed on drying. In a more dilute solution the 

 motile cells were at first green, but as the food became exhausted successive 

 generations became partially, and at last completely, red. A portion of a green 

 culture added to a large bulk of water produced red cells after some days. 

 With increasing strength, above 2 per cent., the cells were motile for a shorter 

 and shorter time, and eventually passed into the non-motile gTeen condition. In 

 a one-per-cent. solution division occurred, but the daughter cells never escaped, 

 and no further development ensued. In solutions above one per cent, no division 

 took place, and the cells remained completely red. 



The size of the cells varies with the concentration of the food substance, 

 being greatest in distilled water and becoming less in successively higher strengths 

 of Knop's solution. In other salt solutions, however, size is not proportional to 

 the osmotic pressure, so that it cannot be supposed that the osmotic factor is the 

 only one at work. 



Palmella-like masses of cells are produced in all cultures in Knop's solution, 

 from 05 per cent, to nearly one per cent., and also in cultivations on damp, porous 

 tiles. 



One-per-cent. Knop's solution is about the highest concentration in which the 

 cells will grow. In considerably higher concentrations they die. 



