Livingston : Chemical stimulation of a gkeen alga 7 



used in such dilution that the slight increase in N0 3 and S0 4 ions 

 caused by the addition could have no effect upon the plant. To 

 test this, variations in the amount of nitrate and sulfate were tried 

 over a greater range than that required for the main series of ex- 

 periments, but without any response in the plant. This is in 

 agreement with the results published previously {loc. cit., 1900), 

 wherein the effect of a decrease of nine-tenths in the amount of 

 any salt in Knop's solution and an increase in the other three 

 main salts sufficient to keep the pressure constant, was found to 

 be without response in the plant. 



Kahlbaum salts were used throughout the work and the 

 utmost pains were taken to have the concentrations correct. All 

 water was distilled in block tin and redistilled in glass. 



Pure cultures of the alga were made in the standard nutrient 

 solution and from these the inoculations were make for the ex- 

 periments. These inoculations were made with wood tooth-picks 

 in place of the usual needle. Sterilization was found not to be 

 necessary, there being no organic bodies in the solutions, and a 

 new tooth-pick was used for each individual culture. Upwards 

 of fifty cultures were usually made at a time, the poison solutions 

 having been prepared in small bottles a day or two before and 

 kept stoppered. The dishes used were the Bausch & Lomb 

 glass culture dishes, about 4.5 cm. in diameter and 2.0 cm. high, 

 with a lid fitting down upon a shoulder after the manner of a pill- 

 box. Ten cubic centimeters of solution were used for each cul- 

 ture. At the New York Botanical Garden the experiments were 

 carried on partly on glass shelves against the pane of an east 

 window, partly in a cool experiment house, and partly on tables 

 directly under a large skylight. At the Hull Laboratory they 

 were placed on glass shelves against a west window. The alga 

 does not require strong light and grows best at a comparatively 

 low temperature. Thus an east or west window of a ordinary 

 laboratory room is well suited for its growth. Cultures came to 

 maturity somewhat earlier in the experiment house than in the 

 laboratory. An experiment ran from twelve to twenty days, 

 being examined in the dish, with the low powers of the micro- 

 scope at critical times, — every day or two for the first few 

 series. 



