——— i —————=—=— ee ee 
1907] JENSEN—TOXIC LIMITS AND STIMULATION 29 
The data show an increasing growth with the increase in amount of 
sand present. This agrees with TRUE and OGLEVEE’s results. At 
the end of the experiment the solutions in which the plants had 
grown were carefully titrated with NaCl, giving the following results: 
Sand about 8°™ high, no trace. 
Sand about 10°™ high, no trace. 
Sand filled bottle, no trace. 
. Sand filled bottle, no trace. 
T endeavored to make quantitative determinations, and thus defi- 
nitely to settle the absorptive power of a given quantity of quartz, 
and at the same time the relation of the amount of silver to length 
of plant grown therein. My attempts, however, were unsuccessful. 
The solutions from the above experiment were filtered free from 
sand, and again used for solution culture in small black bottles 
(70°°) with the following results: 
1. Gave no elongation of root or stem. Roots and base of stem dark brown. 
- Stems slightly elongated. Leaves very much etiolated. Roots long and 
hy. 
a dala os ale ae 
~ 
to 
- About like 2. 
- Stems healthy. Leaves green. Roots white, long and healthy. Av. 
size 7.9°™ 
Ww 
- Same as in 4. Average length of sprout 8.3°™. 
- Soil extract from previous experiment insufficient for this test. 
- Soil extract from previous experiment insufficient for this test. 
In order to test still further the absorptive power of the quartz, a 
Series of cultures, each containing the same quantity of sand and 
Solution, were set up. The difference here was that each culture had 
a different strength of solution. _The quaatity of sand used for each 
Was 270 grams, and of solution 400 grams. The concentrations are — 
indicated in table IX. - ee SOS ees 
TABLE IX 
“SN 
EXPERIMENT To SHOW EFFECT OF QUARTZ UPON DIFFERENT CONCENTRATIONS 
or AGNO; - 
n n 
La wd aes 
nos Too 500 2500 12500 62500 
Average length of s * 8 0-4 10.2 13.9 
Of sprout, cm... +s ae 5 
Ec psig Weight, mg......:. 255 230 _ = 
otal weight, Lo Sy re 67 47 
Se os) pata VS Gis te weer a 
*Dead. 
