42 BOTANICAL GAZETTE [july 



During the gas flow, the odor of gas was evident only at the 

 point where the tube entered the soil. In order to determine 

 whether the gas might be detected by a more delicate means, the 

 etiolated sweet pea seedling test, as described by Knight and 

 Crocker (7) was tried. When the seedlings were 1.5-2 cm. high, 

 the petri dishes containing the seedlings were taken to the Ailanthus 

 tree, placed directly on the soil, and the 10-liter cans inverted over 

 them. The cans, each with a dish of seedlings beneath, were 

 numbered and placed, with reference to distance from the point 

 of entrance of gas, as follows: no. 1, 5 cm., toward tree; no. 2, 

 0.6 m., at base of tree; no. 3,0.8 m., also near tree but on side 

 opposite no. 2; no. 4, 1.2 m., on side directly opposite point of 

 entrance of gas; no. 5, 3 m., as no. 4. The cans were placed August 

 27 and observations were made three days later. The results were 

 as follows: no. 1 gave no growth (observations refer to epicotyls 

 only); no. 2, some growth, with a little swelling; no. 3, growth 

 slightly reduced and diageotropic; no. 4, slender and straight, 

 q-iocm. high (normal); no. 5, as no. 4. These results indicate 

 that the pea seedling probably offers a rather delicate test for the 

 presence of illuminating gas in the soil. In this case the injurious 

 effect on the seedlings was very evident in those placed near the 

 base of the tree, where, as stated before, no odor of gas could be 

 detected in the customary manner. 



In consideration of the great difference in behavior of a given 

 plant when exposed to low and to high concentrations of illumi- 

 nating gas, it seems appropriate to make the following suggestions 

 with regard to the diagnosis of gas injuries. One reason why the 

 foregoing abnormal tissue developments have not been recorded in 

 trees killed by gas is probably the fact that examination was made 

 for pathological symptoms in trees which have died or have become 

 seriously injured. Such conditions would mean that the gas had 

 been at their roots in too high concentration to allow the stimu- 

 lating effects to enter. Sometimes the proliferation reported above 

 was found in roots when no suggestion of injury could be observed 

 in the aerial portions. Therefore, when one is attempting to diag- 

 nose with certainty a serious injury suspected to be due to gas, he 

 ought also to make an examination of roots of other trees in the 

 vicinity which have not yet shown injuries in the leaves, thereby 



