278 
RICHARD M. HOLMAN 
Two methods were employed to assure a sufficient supply of water 
to the seedlings when the roots were kept in air during the course 
of an experiment. In some cases the cotyledons and the older parts 
of the roots were wrapped in wet filter paper or cotton while in other 
cases, the entire seedling, with the exception of the terminal i to 2 cm. 
of the root, was planted in moist soil in a pot through holes in the wall 
of which the ends of the roots projected. At the place where they 
passed through the wall of the pot, the roots were wrapped in narrow 
strips of moist filter paper. All roots cultivated in air were frequently 
sprayed and the atmosphere around them was kept as nearly saturated^ 
as possible by lining the bell jars or other receptacles in which the 
cultures were kept with wet filter paper and in addition by maintaining 
as constant a temperature as possible. 
When the object of an experiment required that the position of a 
root in air be changed after it had been under observation for some 
time, the seedlings were mounted on corks, each of which was cemented 
somewhat eccentrically in a shallow crystallizing dish. These dishes 
were closed with glass plates held in place by wire spring clamps and, 
as far as was possible without interfering with the observation of the 
roots, were lined with wet filter paper. The crystallizing dishes were 
kept on edge throughout the experiment. This was easily accom- 
plished by fitting them into open rings of galvanized metal fastened 
to blocks of wood. During the intervals between observations the 
cultures were placed under bell jars or in zinc boxes lined with wet 
filter paper. 
In every experiment, unless a statement to the contrary is speci- 
fically made, the seedlings were kept in darkness between observations 
and when they were inspected care was taken not to expose them to 
the light for any considerable length of time. In every experiment in 
which the behavior of two sets of roots under different conditions was 
compared, the roots of the two series were carefully matched as to 
length and other visible qualities before they were used ; that is to say, 
each root in one series was of the same length and of approximately 
the same diameter and general appearance as the corresponding root 
in the other series. 
Seedlings whose roots were to be under observation while growing 
in soil, sand, sawdust or other more or less consistent mediums were 
planted in Sachs's boxes or in similar boxes with parallel glass walls, 
when the experiment involved the complete inversion of a culture or 
