1907] JENSEN—TOXIC LIMITS AND STIMULATION 19 
creases until the death point is reached. By the death point is 
not meant that concentration at which all elongation of root or sprout 
from the very first is inhibited, but that which kills the plant when 
the stored food of the seed has been exhausted. Thus it was found 
that after 5 to 10 days plants which at first grew well lost their vigor 
and turned yellow. 
The criteria used for comparing the effect of the substances 
tested are: first, the total transpiration from each pot or culture; 
second, the average length of the sprout; third, the green weight; 
fourth, the dry weight of plants in a pot. 
he curves are as follows: The unbroken line is the average 
length of the sprout; the broken line is the total transpiration; the 
dotted line is the green weight; and the dot-and-dash line represents 
the curve of the dry weight. 
COPPER SULFATE 
In the solution series plants all die in m/1ooo strength and do 
very badly in 52/100000. There is no indication of any stimulation, 
as the control in distilled water has grown more than any other set. 
In the series where 50%™ of 5/o quartz sand is added to an equal 
weight of solution, that is, where the quartz stood half way up the 
column of liquid, we find the wheat growing in /1ooo and not 
altogether dead in 4n/1ooo. The toxicity has evidently been reduced. 
In the series where go%™ quartz to 25*™ solution is used, i. e., the 
solution stands about a centimeter above the surface of the sand, 
the toxic effect has been still further reduced. The killing point 
Now lies between 4n/100o and 8/1000. In the soil series, i. €., 
where 12. 5 per cent. of solution is present, the death point lies be- 
tween 2/100 and 3n/too. It will be evident, therefore, that the greater 
the ratio of quartz to the poisonous solution, provided this does 
not exceed the optimum water content for growth, the less the toxic 
effect of the copper sulfate. Fig. 1 represents a CuSO, series in 
soil six days after planting. The series is close, running from left 
to right n/10, gn/100, 8n/100, 7n/100, 6n/100, sn/100, 4n/100, 
3n/t00, 2n/100, n/too, gn/1000, 8n/1000, 7n/ 1000, 6n/1000, 
5n/ 1000, 4n/1t000, 3n/1000, 2n/1000, m/1000, n/ 2500, n/ 5000, 
n/7500, n/10000, control. It shows that up to 32/100 all elongation 
is inhibited. Beyond this point it shows a rather uniform increase 
