jan. 17,1916 Effect of Sulphur and Calcium Sulphate on Plants 775 
This experiment was repeated, using soil solution in place of Ashby's 
solution. For this purpose 1 kgm. of Miami silt loam was placed in a 
large container, 1 liter of distilled water added, and the entire mass 
boiled for one hour. It was next filtered, and 0.05 gm. of dipotassium 
phosphate and 1 gm. of mannite were added. This was then put into ten 
500 c. c. flasks and 30 gm. of quartz sand added. Various amounts of 
calcium sulphate were used. The flasks were sterilized, and when cool 
were inoculated with a pure culture of red-clover bacteria. All cultures 
were incubated at 23 0 C. At intervals of one, two, and three weeks bac¬ 
terial counts were made. These results are given in Table VI. 
♦ 
Table VI. —Effect of calcium sulphate on the growth of red-clover organisms in soil 
solution 
Number of organisms per cubic centimeter of 
solution after— 
Treatment. 
0 day. 
7 days. 
14 days. 
36 days. 
TTritreated. 
180,000 
180,000 
180,000 
180,000 
180,000 
63,000,000 
135,000,000 
125,000,000 
125,000,000 
138,000,000 
145,000,000 
176,000,000 
178,000,000 
269,000,000 
185,500,000 
146,000,000 
237,000,000 
244,000,000 
259,000,000 
262,000,000 
Given o.oi per cent of calcium sulphate.. 
.02 per cent of calcium sulphate. 
.05 per cent of calcium sulphate.. 
. 10 per cent of calcium sulphate. 
From the data it is evident that the addition of calcium sulphate stimu¬ 
lates the growth of red-clover organisms in pure cultures to the extent 
of more than 100 per cent. The results of this test agree with those 
obtained in Ashby's solution—i. e., that small amounts of calcium sul¬ 
phate are apparently as beneficial as larger amounts. 
EFFECT OF SULPHUR AND SULPHATES ON HIGHER PLANTS IN 
ARTIFICIAL MEDIA 
Various experiments were made with the view of determining the 
effect of calcium sulphate and sulphur upon the growth of clover and 
upon nodule formation. This was tested first in artificial media. The 
medium consisted of a soft synthetic agar prepared from 1 liter of tap 
water, 5 gm. of dipotassium phosphate, and 7 gm. of agar. This medium 
was sufficiently firm to support the seeds. Thirty c. c. of the melted agar 
plus various quantities of calcium sulphate were added to each of 50 
test tubes. In order to reduce the individual variation between the 
plants, 10 parallel tubes were used. The tubes were sterilized, and then 
two seeds of red clover were planted in each. After inoculation the 
cultures were removed to the greenhouse. At the end of two weeks 
greater root development was noted in the calcium-sulphate test tubes 
than in the untreated ones. In the older plants the increase in root 
development became most marked. The tops, however, failed to show 
any difference in size. In the tubes to which 0.1 per cent of calcium 
sulphate had been added, the plants were slightly smaller than the 
