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. 1 



C. THE EFFECTS OF ILLUMINATING GAS ON ROOTS IN SOIL MEDIUM 



i. Quantitative tests 



a) Calalpa speciosa seedlings; illuminating gas; exposure 

 period 8 days; concentrations 1:2000, 1:400, 1:200, 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. 



6) Same as above, with the exception of ethylene in place of 

 illuminating gas but in corresponding concentrations (that is, 

 1:50,000, 1:5000, 1:1000, and 1:500). 



No effect on stems or leaves. The responses with concentra- 

 tions 1 : 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, 

 fig. 1). 



c) Catalpa seedlings; illuminating gas; duration of exposure 

 21 days; concentration 1:4 and controls. 



Stem and leaves gave no response. Roots oi 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 



1 Perhaps this could be accomplished by passing pure air through the soil by 

 means of a pipe thrust below the surface. 



