38 BOTANICAL GAZETTE [JULY 
and B respectively of fig. 6. Through an examination of figs. 5 
and 6 it becomes evident that the stelar region has remained un- 
changed, while the cortex, 
extending to the phellogen 
layer, has increased in 
thickness, partly through 
increase in the diameter of 
the cells, and partly 
through cell division. At 
the phellogen layer of the 
Ss treated root, cell division 
A) has been rapid, resulting 
yy) in the production of a 
ees loose tissue not present at 
San all in the normal. The 
A stee B tissue lying outside the 
va 
x 2 
A) 
O 
phellogen layer in the 
beginning has been only 
slightly modified in the 
abnormal root. 
f) A number of tests 
: F °: were carried out with 
Fics. 4, 5.—Fig. 4., section through the cortex Gleditschia seedlings, used 
of tap root of Catalpa: A, control; B, treated in illuminating gas in 
with illuminating gas; fig. 5,same for Ailanthus various concentrations up 
roots, showing detail of the tissue regions out- : z 
Wied im fa 6 cae, fo" ats (concentrations 
higher than 1:3-1:4 were 
not used for fear of oxygen becoming a limiting factor). Concen- 
tration 1:3 gave leaf fall, but no definite injuries were detected in 
the root system. 
i, 
LA 
@ 
( }s 
é: 
2°6°-0@ 
ete 
stews 
ee: 
ox 
2. Qualitative tests with potted woody plants 
When illuminating gas was passed rapidly through the soil of a 
potted plant, injuries might be observed the first day and death 
in all cases in the course of afew days. This is not at all surprising, 
because one should expect injury and final death to result as an 
effect of the shutting off of the oxygen supply, even though an 
