1907] JENSEN—TOXIC LIMITS AND STIMULATION 17 
All salts used for nutrient media, as well as those used as poisons, 
were Kahlbaum’s C. P. grade. 
The ordinary distilled water of the laboratory was re-distilled in 
glass flasks. From this redistilled water all solutions were made. 
Methods 
Preliminary experiments for the determiaation of the optimum 
water conteat of the quartz were first carried out with redistilled 
water and with nutrient solution. It was found that 12 to 15 per 
cent. by weight of water was best. 
The wheat seeds were germinated in sphagnum aad in quartz. 
It was found that the sphagnum was more satisfactory, because 
foreign particles could be more easily removed from the roots at 
transplanting. Transplanting was done when plants had attained 
a maximum height of 3°. 
Three hundred and thirty-six grams of quartz were weighed out 
for each culture basket. This was mixed with 42°° of solution, thus 
making 12.5 per cent. of moisture content. This damp soil was 
then packed in the basket, and with the culture series completed, 
all were planted with plants as nearly alike as possible. The plants 
(five in each pot) stood in a straight line and protruded through a 
slit in the paraffined paper cover. The latter was then sealed to 
the sides of the pot with melted paraffin. The pot was labeled 
with the strength of solution it contained and the weight. The 
slit through which the plants protruded was loosely plugged with 
ordinary cotton, so that the loss of weight was practically reduced 
to the transpiratioa by the plants. After two or three days the 
pots were put oa the seale-pan, the original registered weight was 
placed on the opposite pan, and a balance obtained by adding to each 
some solution of its own strength from a pipette. Thus the weight 
Was again made what it was at the time of planting. This was 
done as often as needed; at first each two or three days; afterward, 
as plants got larger, every day. In this way the amount of water 
Was never more than 12.5 per ceat. and probably aever less than 
TO per cent. The amounts added were recorded, and their sum 
Constitutes the total transpiration for a pot as recorded in the tables. 
t the end of the experiment, usually in 15 to 30 days, the longest 
