130 BOTANICAL GAZETTE [AUGUST 



formula 4 as follows: iooo cc NaCl, 3^/8; y8 cc MgCl 2 , 3^/8; 3 8 CC 

 MgSO 4 , 3^/8; 22 CC KC1, 3^/8; io cc CaCl a , 3 w/8. s 



This closely approximates the bay water. The plants thrive 

 almost as well in it as in sea water, especially when a very little 

 NaHCO 3 or KHCO 3 is added to produce a neutral or faintly alka- 

 line reaction. 



A series of solutions was tried, beginning with pure NaCl 3^/8 

 and adding to it in turn MgCl 2 , KC1, and CaCl 2 , either singly or in 

 combination, in the proportions given above. These salts were also 

 used in pure solutions of the same concentration at which they exist 

 in the artificial sea water described above. 



It should be said that little difficulty was experienced in deter- 

 mining the death point with sufficient precision. The color reactions 

 and the microscopic appearance of the cells allowed this to be done 

 with sufficient accuracy, so that the results were not in doubt on this 

 account. 



The results of the experiments are set forth in the tables. The 

 figures represent the average of four parallel series carried on simul- 

 taneously. A control series was also carried on in which each solu- 

 tion was made faintly alkaline by the addition of NaHCO 3 , KHCO 3 , 

 or Ca(OH) 2 . This had a beneficial effect during the first two or 

 three days of the experiment, but the final results were practically 

 the same as in the other series. 



From a consideration of the results for Group i we may draw 

 the following conclusions. 



i. The plants die much sooner in a pure sodium chlorid solution 

 (isotonic with sea water) than in distilled water. The poisonous 

 effect of the NaCl largely disappears if we add a little CaCl 2 (io cc 

 CaCl 2 3^/8 to iooo cc NaCl 3^/8) ; in this mixture the plants live 

 nearly as long is in distilled water. Addition of KC1 to this mix- 

 ture enables them to live longer than in distilled water. Further 

 addition of MgCl 2 and MgSO 4 enables them to live practically as 

 long as in sea water. 



4 VAN'T HOFF, J. H., Physical chemistry in the service of the sciences 101. Univ. 

 of Chicago Press, 1903. 



s This corresponds approximately to the proportion of Ca in the sea water of 

 the bay. 



