512 Townsend . — The Correlation of Growth 
been determined, a shallow dish containing 200 cc. of water, 
in which a definite amount of ether had been dissolved, was 
introduced under one of the bell-jars, the other preparation 
being left in a normal state for control. In some of the 
experiments the seedlings were kept in a dilute atmosphere 
of ether as long as they continued to grow, while in other 
cases they were placed in a strong atmosphere of ether for 
a short time. In order to measure the leaves, it was necessary 
to remove the plants from the bell-jars from time to time ; 
and, as this allowed more or less of the ether to escape, a fresh 
mixture of ether and water was introduced under those 
bell-jars in which it was desired to maintain a constant 
atmosphere of ether. 
Older Plants . — In preparing the older plants, seedlings 
were first started in damp sawdust, and then transferred to 
pots of damp earth and kept for several weeks under bell- 
jars. In order to have the root-tip in view, the main root 
was directed through the hole in the bottom of the flower-pot 
and allowed to extend into a damp chamber. 
To study the growth of the root after the stem was injured, 
the root was marked 15 mm. from the tip, and the normal 
rate of growth observed. Only a part of the stem and a few 
of the leaves were then removed, and the growth of the root 
noted from time to time. 
In considering the influence upon the stem when the roots 
were injured, a knife-blade 5 2 cm. in length was passed 
around the main root at a distance of only a few centimeters, 
thus severing a larger or a smaller number of the secondary 
roots. In order to determine accurately the degree of injury 
which was inflicted by removing the roots, and also to 
eliminate the influence of transpiration, seedlings were placed 
in cylinders of plaster of Paris from three to four centimeters 
in diameter, the bottoms of which were composed of cotton- 
netting. The netting prevented the earth from falling through, 
but allowed the roots, which were directed into damp 
chambers, to pass freely. By this means a definite number 
and desired length of roots could be removed. Calla plants 
