[Vol. 2 



478 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



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V. Recovery of Plants after being in Toxic Solutions 



Having thus ascertained the maximum time plants may 

 remain in distilled water and then recover on being placed in 

 full nutrient solution, we may turn our attention to toxic 

 solutions. If distilled water in itself is toxic then it should 

 be interesting to get quantitative data on its effects as 

 measured by the power of plants so treated to recover. This 

 power should furnish a good index regarding the extent of 

 any injury suffered. By comparing the ultimate time limits 

 for various media after which recovery in full nutrient solu- 

 tion is possible, we are able to get a basis on which to de- 

 termine the relative toxicity of each medium. Almost simul- 

 taneously with series 3, series 4 was set up. The plan of 

 the series and the green weight of tops and dry weight of 

 roots of the plants in series 4 are given in table vi, while pi. 15 

 fig. 2 shows the actual condition of the plants in some of the 

 media. The results obtained indicate the followin 

 toxicities of the substances used, the time expressed in days 

 having reference to the longest period in the toxic solution 

 after which recovery is possible : 



Redistilled water 30-40 days 



N/100 MgCl 2 4-8 da y s 



N/1000 MgCl 2 about 20 days 



N/1000 CaCl 2 & N/20 MgCl 2 about 16 days 



N/12800 H 2 S0 4 about 20 days 



N/400 KOH about 20 days 



We thus see that as compared with the toxic solutions men- 

 tioned distilled water, if it be considered as a toxic 

 all, is much less so than either of the others given above. In 

 this connection it is interesting to note that Kahlenberg and 

 True ('96) found that N/12800 H 2 SOi and N/400 KOH were 

 approximately the critical concentrations for Lupinus roots. 

 Hence, the fact that plants can remain much longer in distilled 

 water than in these solutions and still recover would seem to 

 indicate that as regards toxicity distilled water is only very 

 slightly if at all deleterious. But the writer believes that it 

 is entirely incorrect and misleading to speak of distilled 

 water as being toxic. What is illustrated above for distilled 

 water is not toxicitv, therefore, but merely the length of time 



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