140 GROWTH OF PLANTS 



The greenhouse operator had lost the carnation crop in several of his 

 greenhouses each fall for two years after a cold spell had frozen crust on 

 the ground. Near the greenhouses affected was a honey-combed illuminat- 

 ing gas pipe. When there was no crust on the ground the gas escaped 

 upward into the air. With a frozen crust on the ground the gas moved 

 horizontally and escaped into the greenhouse. With the ventilators closed 

 during the cold spells the gas was held in the houses. 



Crocker and Kjiight "^ tested the effect of the Chicago illuminating gas 

 (a water gas) on carnations. The buds and flowers proved most sensitive. 

 One part of illuminating gas to 40,000 of air stopped the growth of young 

 and medium-aged buds, and 1 : 80,000 caused freshly opened flowers to close, 

 "go to sleep," within 12 hours, and they wou^d not open again even in 

 absence of the gas. As manufactured illuminating gas is a mixture of many 

 gases, the question naturally arose, Which of the constituents are effec- 

 tive? Neljubow ^^ had previously investigated the reason for the peculiar 

 growth of certain plants in "laboratory air" and found it due to a trace of 

 illuminating gas. He found that ethylene produced the "horizontal nuta- 

 tion" of the garden pea epicotyl in concentrations as low as 1 ppm of air. 

 The ethylene in the air changed the geotropic equilibrium position of the 

 garden pea epicotyl gradually from the vertical to a more and more declined 

 position as the concentration of ethylene increased, until 1 ppm of ethylene 

 brought the tip of the seedling into a horizontal position or made it diageo- 

 tropic. Fig. 51 shows the results of repeating Neljubow's experiments 

 43 years later upon another variety of garden pea. The controls show the 

 great amount of elongation in the epicotyls in three days, and also that 

 they are negatively geotropic, i.e., grow vertically. One ppm of ethylene 

 reduced the rate of elongation markedly, caused the portion of the pea that 

 grew w^hile in the gas to take a declined position; 1.33 ppm reduced the 

 elongation much more and caused the part gro\\ang while in the gas to 

 become diageotropic and the gromng part to increase in diameter; and 

 4 ppm reduced elongation still more, with a consequent shorter swollen 

 and diageotropic region. It is interesting that these results check so closely 

 with Neljubow's, although a different variety of pea was used under a 

 different set of conditions. He got horizontal nutation in 1 ppm of ethylene; 

 Crocker and Knight got it mth 1.33 ppm of ethylene. They found further 

 that 1 ppm of ethylene prevented the growth of young carnation buds and 

 0.5 ppm of ethylene caused open flowers to close. 



From this work Knight and Crocker concluded that ethylene was the 

 effective constituent of illuminating gas in bringing about the injury to the 

 carnation buds and flowers. The crude methods of analysis available at that 

 time indicated that the gas bore about 3 per cent ethylene, whereas it 

 should have borne 4 per cent according to the flower and bud response. 

 The discrepancy can be explained by errors in analysis and variation in 

 the sensitivity of the buds and flowers, as well as variations in the ethylene 

 concentration of the gas. Later work has also shoAvn that, while certain 



