ACID-SOIL PLANTS—COVILLE 371 
and many of them died. Sulphate of aluminum was applied to 
similar plants in the same soil. The result, with one excep- 
tion, was a definite and pronounced stimulation of growth. The 
exception was an experiment in which the aluminum sulphate was 
applied in a very strong solution, one-third gram of the ground sul- 
phate in 1 cubic centimeter of water (M/2). This solution was so 
strong and the small seedlings, previously in active growth, were 
so delicate that about half of them were immediately killed. The 
surprising and significant feature of this experiment was that the 
seedlings that survived showed later the same stimulation of growth 
as those that were treated with milder solutions. The applications 
ranged in amount and strength from that cited above down to 10 
cubic centimeters of a 0.57 per cent solution (M/60). The illus- 
tration of one of these experiments, in Plate 3, will suffice for all of 
them. 
The next experiment to be described related to the possibility of 
resuscitating a sickly rhododendron in an ordinary garden soil by 
the application of sulphate of aluminum. On June 3, 1922, eight 
plants were selected from a large number that had been potted on 
May 3, 1921, in 2-inch porous earthenware pots in the fertile garden- 
soil mixture already described. For more than a year the plants had 
been stagnant and sickly. To each of four of the pots was applied 
half a gram of ground aluminum sulphate. The material was spread 
on the surface of the soil and dissolved and washed down with water. 
The other four plants were left untreated. All eight plants were 
plunged in sand and received afterwards the same greenhouse 
treatment. 
After seven weeks a small amount of growth had taken place in all 
four of the aluminum-sulphate plants, barely enough, however, to 
be conspicuous in a photograph. The four untreated plants had 
made no growth. 
As the effect of the aluminum sulphate was clearly beneficial, but 
slower than in the earlier experiments, it was decided to make a 
further application. On July 27, 1922, an additional half gram of 
aluminum sulphate was applied to each of the four plants to which 
the earlier application had been made. 
On August 30, when the photograph reproduced in Plate 4 was 
made, 11 weeks after the beginning of the experiment, the dif- 
ference between the two lots of plants was conspicuous, not merely 
in their size but still more in their color and texture. The aluminum- 
sulphate plants had made an increase of about 65 per cent in the 
diameter of their rosettes, and their leaves had the delicate texture 
and bright green color of plants in active and healthy growth. The 
untreated plants had made no growth. They were very sickly, their 
leaves a dull reddish-green color. The resuscitation of the four 
