Livingston : Chemical stimulation of a green alga 



5 



are given in terms of a normal solution, i. e., one gram equiva- 

 lent per liter of solution.* The osmotic pressure data are com- 

 puted from A,, the lowering of the freezing point below that of 

 distilled water f, measured in Centigrade degrees. 



Formula and osmotic pressure of nutrient medium 



The above solution was made up from normal solutions of the 

 component salts. Practically no Ca 3 (POJ 2 is precipitated if the 

 K.,HP0 4 is added to the other salts only after the addition of 

 nearly all the required water. 



In the control medium just described the alga takes the fila- 

 mentous form, and zoospores are plentiful. For the palmella 

 form a solution of one hundred times the strength of this was used. 

 The iron salt, however, was not increased in amount. 



On account of the extreme complexity of the general question 

 of toxic stimulation, it seemed expedient to work with but one of 

 the two forms of this alga. By the use of poisons it has been so 

 far impossible to cause a strong solution to produce other than 

 the palmella form, but weak solutions can be made to produce 

 this form at will, as will be shown in this paper. Therefore the 

 filamentous form was chosen as the most responsive and thus the 

 best suited to the work in hand. 



On account of the well-known toxicity of certain metals, and 



* Throughout this paper the decimal system will be used to denote fractions of 

 normal solutions rather than the cumbrous method of dilutions by one half commonly 

 in use by chemists. One is easily reducible to the other, but it seems that for modern 

 workers the decimal system is by far the better. The form of the common fraction is 

 retained on account of a somewhat greater ease of reading. 



f For the method of making this calculation, see Livingston, B. E. The r61e of 

 diffusion and osmotic pressure in plants, 37 (Chicago, 1903), and the references given 

 on that page and at the beginning of the volume. The osmotic pressure, in milli- 

 meters of mercury, of a solution at 25 C. ( P 25 ) is approximately given by the formula : 

 P 25 =Io,Ol4.84 A/. This quantity in terms of M (22.3 atmospheres, the calculated 

 pressure of a molecular solution of a non-electrolytic and non-hydrating body) is given 

 by the formula : P 25 =o.59 A,-. 



