﻿96 



BOTANICAL GAZETTE 



[FEBRUARY 



reading, without accompanying information on the toxicity of 

 the chemicals used. By the fragmentary condition of our 

 knowledge on this subject, I have been obliged to determine for 

 myself the toxicity of these substances for the different organ- 

 isms, and have compiled tables on the tadpole, Callitriche, and 

 Elodea, of which the two former may be omitted, with the 

 corresponding statistics on respiration. These experiments on 

 Elodea were made with young growing tips, 2-4^°^ ^oi^g- The 

 condition of the plant, dead or alive, was determined by trying 

 to plasmolyze the youngest grown leaves in KNO3. Relieved of 

 details as to concentrations which do not seriously injure or are 

 stronger than enough to kill, the results follow, the figures being 

 the number of liters of solution in which one gram-molecule is 

 imagined distributed. 



Pb(N03)2 Alive but hardly sound after 24 hours in 



in 



M 

 25 



M 



10 



Appears normal 



KCN 



Dead in 30 hours in 



M _ ,. . M 



, but alive in - 



KOH 



Dead in 2 hours in 



100 

 M 



200 



100 



: in one test dead, in another almost so 



after 24 hours in 



M 



200 



NiCl 



Dead in 24 hours in - — : somewhat unsound in - 



100 



200 



ZnS04 



Dead in three hours in 



M 



100 



: alive but unsound after 26 hours in 



M M 



: sound indefinitely in 7^, below 20" C. 



200 



500 



HCl 



Dead in 15 hours in 7^ : unsound after 24 hours in 



CoCl 



500 



Practically dead after 24 hours in 



1000 



M 



10,000 



Cd(N03)2 Almost dead after 24 hours in 



M 



20,000 



CuSO 



M 



HsrCl^ 



Dead in 25 hours in - 



•^ 20,000 



M 



Sound after 5 hours in 



: alive in 



: sound in 

 M 



M 



40,000 



40,000 



M 



AgXO 



Dead in 24 hours in 



40,000 



M 



, but dead in 30 hours in ^ r^ . 



160,000 



: unsound in 



M 



320,000 



These determinations were made at a temperature of about 20" C. 



K is a shade less poisonous than Pb ; Na, a little less still, 



■ 



compared as nitrates. With the tadpoles, Pb and Cd were more 



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