346 THE BIOLOGY OF STENTOR 



was used in the ratio of 500 ml of salt solution to 3500 ml of 

 culture water. The calcium was especially important. Chalkley's 

 solution for amoebas (NaCl, o-ig; KCl, o-oo4g; CaCl2, 0'Oo6g, 

 and 1000 ml glass distilled water) has also been used (Randall and 

 Jackson, 1958), and Hetherington (1932b) suggested 0-06% 

 artificial sea water. Uhlig (unpublished) found that the addition 

 of soil extract and Knop's solution in equal parts produced 

 excellent cultures of coeruleiis. The formula for Knop's is: MgS04, 

 0-25 g; CaNOs, o-ig; K2PO4, o-i2g; KCl, oi2g; FeCls, trace; 

 and 1000 ml of distilled water. In all these additives the guiding 

 principle is of course that essential ions and elements should be 

 supplied in surplus. 



Stentor polymorphus has been cultured in soil extract 

 (HammerHng, 1946) or o-oi% Benecke's solution (Schulze, 1951) 

 with the green alga Gonium tetras as food. Randall and Jackson 

 grew these stentors in Chalkley's solution with added gel from 

 wheat grains boiled in the same. Sleigh (1956) grow polymorphus 

 in a basic medium each liter of which contained inorganic salts 

 measured in millimoles as follows: NaCl (1-4), KCl (0-05), 

 NaHCOs (0-045), CaCl2 (0-035) and CaH4(P04)2.H20 (0-006), 

 made up in distilled water of about pH 6-8. This solution was 

 nutrified with wheat grains and the stentors were fed Chilomonas. 



These cultures are to be kept in the light if the stentors bear 

 symbiotic chlorellae, but too bright an illumination is undesirable. 

 The observation that polymorphus undergoes fission only at night 

 (Hammerling, 1946) suggests the possibility of obtaining simul- 

 taneous division in well-fed mass cultures transferred from light 

 to darkness. 



To the basic fluid medium may be added nutrient materials on 

 which bacteria and other food organisms can live. Hay and hay 

 infusions have not been found satisfactory, perhaps because the 

 culture becomes too acidic. The hydrogen ion concentration should 

 fall between 6-2 and 8-o (Strom, 1926; Belda and Bowen, 1940). 

 Prowazek (1904) used lettuce leaves but he found that his cultures 

 went through periodic depressions. The same, or lettuce extract 

 if cleaner cultures are desired, was recommended by Belda and 

 Bowen. They remarked that cultures should be grown in a darkened 

 place because growth is not satisfactory where abundant green 



