Livingston : Chemical stimulation of a green alga 17 



5»/iOO to ///TOO, with filaments also quite well developed in the 

 last-named strength. Osmotic pressure probably begins to play 

 some part here. The killing concentration was not determined. 

 There is little if any acceleration of zoospore production. Cul- 

 tures appear normal in /z/i,ooo. 



26. Sodium sulfate (Na 2 S0 4 ). — This follows the last-named 

 salt accurately as far as was determined. 



2J. Strontium nitrate (Sr(NO a ) 2 ). — This cation is very slightly 

 toxic, so that here again osmotic phenomena begin to play a 

 part before a stimulating concentration is reached. The killing 

 strength was not determined. The palmella form is produced 

 typically in 5// 100, and there is unquestionably an accelera- 

 tion in zoospore production in 5// '1,000, in which the zoospores 

 develop into short filaments but are destroyed rapidly by the 

 formation of zoosporangia. The cultures are normal at //.' 1,000 

 and below. 



28. Uranyl nitrate (U0 2 (N0 3 ) 2 ). — Death occurs here in 

 «/ 1 0,000 or stronger, the spherical form appears in 5// 100,000 

 and is found mixed with filaments in // '100,000. Acceleration of 

 zoospore production is exhibited in // 100,000 and in 5// 1,000,000, 

 while normal growth occurs in n\ 1,000,000 and below. 



2g. Zinc nitrate (Zn (N0 3 ) 2 ). — In 5/// 10,000 death ensues, in 

 ;z/iO,000 about one half of the cells die, the rest take the palmella 

 form. In 5/// 100,000 both filaments and palmella occur and 

 zoospores are more numerous than in the control, while in ///lOO 

 growth is the same as in the control. 



jo. Zinc sulfate (Zn S0 4 ). — The sulfate of this metal acts like 

 the nitrate, excepting that here again an acceleration of zoospore 

 activity could not be established. 



These results will now be brought together in tabular form. 

 In the table which follows, the salts are arranged in the same order 

 as in the foregoing description. In the first column after the name 

 of the salt, occurs the lowest concentration producing death. In 

 the second column are placed the concentrations at which filaments 

 change to the other form. The strengths at which zoospore pro- 

 duction is accelerated are shown in column four, and that at which 

 growth becomes normal is expressed in the last column. 



