EXPERIMENTAL STUDY. 43 
The uniformity in the favorable results with the different lime salts 
in overcoming the poisonous effects of an excess of magnesia indicate 
that the action was due to the basic and not to the acid radical. 
Should there be a favorable action of the acid radical in this relation 
it would appear in cases where a magnesium salt was employed with 
such an acid radical. The uniform toxic effect of the magnesia in 
excess without lime, and the elimination of that effect in the presence 
of lime, indicate that the acid radical of the salt has none or at least 
very little influence in the matter aside from favoring solubility, as 
further experiments prove. Lime appears to be the only antidote, as 
far as the elements were tested, for combating an excessive amount of 
magnesia. 
LIME AND MAGNESIA AS CARBONATES IN SAND CULTURE. 
In order to further study the relation of lime and magnesia to each 
other in their effect upon plant growth other experiments were 
planned. 
To 60 kilograms of clean, white quartz sand there were added the 
following compounds: 
Per Gent: 
ees De ea Oe a ee ae ee 0. 4 
en rr rs ee ee ke het oe cee 0.2 
eer Ce ee ee a a SS DS ee ce 0.1 
ES os Seeds eS Ss a ee ea 
To 30 kilograms of the sand there were added MgO as MgCO,, 0.1 
per cent; and to the remaining 30 kilograms, MgO as MgCO,, 1 per 
cent. The chemicals were rubbed up in a mortar, added to a small 
portion of the sand, and then to the whole amount. The sand was 
put into twelve pots, holding 5 kilograms each. Those with the 
minimum amount of magnesia were marked /A to 64, inclusive; those 
with the maximum amount, 7 to /2B, inclusive. 
EXPERIMENTS WITH TOBACCO. 
. In the first series, marked A, the portion of CaO to MgO was 15 
tol. In the second series, marked £4, the porportion of CaO to MgO 
was 3 to 5. On January 6, tobacco plants 5 cm. high were taken from 
rich soil, the roots carefully washed, and were set in the sand. A 
nutrient solution was made up consisting of KNO,, 10 per cent; 
NH,NO,, 10 per cent; H,KPO,, 1 per cent. There was added each 
week to each pot 1 ¢. ¢. of this solution. 
The plants in the A pots continued to grow, were of normal appear- 
ance, and good color. The plants in the B pots ceased growing after 
they were planted; the lower leaves turned yellow and died, the upper 
contracted, became thickened and wrinkled, and acquired a deeper 
shade of green. 
