36 BOTANICAL GAZETTE [JULY 
or ethylene. If we consider here also the results of the first series 
of experiments, it would seem that the chief causes of injury to root 
systems are those constituents of illuminating gas which are present 
mainly in the interstices of the soil, rather than those dissolved in the 
soil water. 
The greatest danger in replanting where other plants have been 
killed by gas, seems to lie in the constituents remaining between the 
soil particles. If, therefore, a method was devised for quickly 
aerating this soil, trees might be safely planted at once without 
removing large amounts of soil." 
C. THE EFFECTS OF ILLUMINATING GAS ON ROOTS IN SOIL MEDIUM 
1. Quantitative tests 
a) Catalpa speciosa seedlings; illuminating gas; exposure 
period 8 days; concentrations 1:2000, 1:400, I:200, 1:40, 1:20, 
and controls. 
Stems and leaves showed no modifications; neither were there 
any strongly marked effects on the root systems. In concentra- 
tions 1:40 several roots gave indications of swelling 1-2 cm. back 
of the tips, while in concentrations 1:20 these swellings were very 
evident. 
b) Same as above, with the exception of ethylene in place of 
illuminating gas but in corresponding concentrations (that is, 
I 50,000, I: 5000, 1:1000, and 1: 500). 
No effect on stems or leaves. The responses with concentra- 
tions I: 1000 and 1:500 were like those above, but in addition, the 
tendency of the roots to coil at the tips (as noted in Vicia Faba, 
ea). 
c) Catalpa seedlings; illuminating gas; duration .of exposure 
21 days; concentration 1:4 and controls. 
Stem and leaves gave no response. Roots of 1:4 gave swelling 
of main root extending from near the surface of the sand 4-7 cm. 
downward (fig. 3). This increase in amount was 2-3 times that 
of the normal thickness. The epidermis was often cracked and 
sloughed off in places. The drawing of fig. 4 shows that the swelling 
* Perhaps this could be accomplished by passing pure air through the soil by 
means of a pipe thrust below the surface. 
