148 GROWTH OF PLANTS 



has given a very sensitive and exact means of detecting the presence or 

 absence of the gas in the greenhouse. This and various other detrimental 

 changes caused in plants by traces of ethylene have been impressed upon 

 the minds of both the greenhouse o^vners and the gas companies. As a 

 result, the greenhouse owners now recognize gas injuries in their incipiency 

 and, what is more important, the gas companies take great care in testing 

 for leaks and repairing them in the neighborhood of greenhouses. 



There is one precaution that has not received enough attention, namely, 

 the trapping of water drains from greenhouses. We have observed cases 

 where gas leaks several blocks from a greenhouse caused injury. The gas 

 escaped into the storm sewer, traveled through it, and into the greenhouse 

 through the untrapped drainage tile. Water drainage lines from green- 

 houses should have cemented joints so as to be air-tight. They should also 

 have a trap outside the greenhouse ^\dth an upright vent outside the trap. 

 While this would prevent injury lq some cases, ia many others it would not. 

 Gas mil seep many rods thi^ough the ground under a frozen crust and 

 escape up into the greenhouse through the unfrozen ground. The real way 

 to prevent injury is to see that there are no gas leaks even in the general 

 neighborhood of a greenhouse. The epinastic response has been used in 

 submarines ^ to determine whether any exhaust gases are escaping into 

 the hull. 



This test even has its place in home and social adjustment. The local 

 gas company had trouble in convincing two lady school teachers that there 

 was not a gas leak in their apartment. The ladies were sho^vn that the 

 tomato could detect about Mooo the least concentration the human nose 

 could detect. The tomato plant indicated no gas in the apartment. The 

 teachers agreed that they were smelling something else. The author gave 

 a judge's wife a beautiful Crassula arhorescens plant. After it had been in 

 the house two weeks many of the leaves had fallen. The tomato plants 

 indicated leaks in the 20-year-old gas stove, but a much bigger leak in the 

 gas meter under the front room. The judge's wife got a new stove and the 

 gas company repaired the meter. The judge heard from his neighbors for 

 his penuriousness in failing to buy a new stove until the evidence was 

 overwhelmingly against him. Oort\njn Botjes ^^ used the epinasty of 

 tomato leaves to show that ripening apples produce ethylene. Other inves- 

 tigators 16, 25. 26, 55 have used epmasty in tomato, potato, and marigold 

 leaves and horizontal nutation in the pea seedling to demonstrate ethylene 

 emanations from respiring tissues of several kinds of plants. Many other 

 uses of this response in research will be mentioned below. 



Proliferation of tissues. Ethylene induces the proliferation of plant tis- 

 sue, especially of cork cambium, as well as enlargement of cells. Harvey 

 and Rose ^^ showed that when illuminating gas flowed slowly through soil 

 in which plants grew it caused the development of massive soft white tissue 

 at the base of the stem and on the larger roots of Hibiscus, also on roots 

 and lower part of the stem of Catalpa seedlings. This tissue resulted both 



