184 Deficient Soil Oxygen [382 
the nitrogen it is impossible to be sure that the replacement 
is ever absolutely complete at the beginning of the experi- 
ment. 
The cessation of water intake, as shown by the stoppage 
of absorption from the auto-irrigator, is always the first 
sign of injury. With Coleus and Heliotropium it is followed 
in from one to six days by progressively lessened turgor of 
the shoot and leaves and finally by wilting and death. With 
Coleus, the admission of oxygen to the soil before death has 
actually occurred is followed by the slow recovery of the 
plant. Heliotropium does not so recover, even if oxygen is 
re-supplied before the wilting has become extensive or 
severe. With Nerium oleander, which does not wilt, the 
symptom of injury which follows next after the cessation 
of water intake by the roots is the yellowing and loss of 
leaves. 
On removal and examination of the injured plants the 
root systems are found to be dead and the roots partly dis- 
integrated. When the injury has been slight or recent, in- 
dividual roots are determinately dead only in parts of their 
length, regions of brown discoloration alteraating with re- 
gions of apparently healthy root. When Coleus is first in- 
jured and then revived by re-admission of oxygen it forms 
a new root’ system, the new healthy roots being clearly dis- 
tinguishable from the older dead ones. These new roots start 
always from the base of the stem, as in a rooted cutting. 
They have never been observed to start from any portion 
of the older root system. If one begins with a Coleus plant 
which has a small root system, or with an unrooted cutting, 
or with a previously injured plant which will form new 
roots, it is possible to grow such a plant with a soil atmos- 
phere somewhat below normal in oxygen content. In this 
case the shoot does not attain so large a size as the shoot 
of a normal control plant and is more susceptible to injury 
by drouth, as, for instance, by increase in the evaporating 
power of the air. The root system of such a plant, grown 
with deficient oxygen, is less developed than that of a normal 
