194 GROWTH OF PLANTS 



Turkish tobacco, aster, kidney bean, cucumber, tobacco (A^. glaiwa), 

 salvia, poppy, tomato, clover, radish, calliopsis, and cosmos, slight injury 

 below 40 ppm and severe injury and death above 400 ppm. Temperature 

 is as important as concentration, injury increasing rapidly with increases in 

 temperature. In some cases wilted plants appear less sensitive to hydrogen 

 sulphide injury than normal turgid plants. Plants tested for lime sulphur 

 injury (aster, buckwheat, sunflower, and tomato) showed symptoms iden- 

 tical Avith those produced by hydrogen sulphide." 



Here again injury by H2S differs from injury by SO2 in two respects: the 

 minimum concentration of HoS for injury to plants is many times that for 

 injury by SO2, and wilting of plants furnishes less protection against H2S 

 than it does against SO2. We have already seen that the degree of stomatal 

 opening is an important factor in SO2 injury. Hydrogen sulphide may 

 enter through the cuticle rather than through the stomates, or the young 

 tissues may be much more susceptible to H2S injury than older tissues. 



Effect of Chlorine Gas and Chlorinated Water on Plants 



AND Animals 



The staff of the Institute has been called in on several cases of injury to 

 plants by chlorine gas escaping from tanks used to treat water for swimming 

 pools and on injury to plants by fumes from laundries. The question 

 whether there is enough residual chlorine in the tap water of a city to injure 

 greenhouse plants watered with it, and water plants and fish hving in it, 

 is a perennial question. 



Our observations and unpublished experiments indicate that chlorine 

 gas m the air affects plants much as does SO2. The middle-aged leaves are 

 most sensitive and the spotting of the leaves is similar to that caused by 

 SO 2; also, as reported later in this chapter, CI2 is much more toxic to leaves 

 in clear than in cloudy weather as is SO2, indicating further similarity of 

 behavior between these two gases. It will also be observed that CI2 in the 

 air spots leaves in even lower dosages than SO 2. It is also more toxic to 

 animal pathogens and about equally toxic to plant pathogens. Our un- 

 published experiments likewise proved leaves more sensitive to CI2 than 



to SO2. 



Zimmerman and Berg ^^ ran extensive experiments on the effect of 

 chlorinated water on land and water plants and on goldfish. Land plants 

 proved rather resistant to chlorinated water, but water plants were sensi- 

 tive. The authors summarize their results on plants as follows: p"^"''^ 

 "None of the species of plants grown in loam soil and watered, syrmged, 

 or watered and syringed with chlorinated water having 50 ppm or less of 

 chlorine in water, were injured or retarded when grown in pots in cold 

 frames, on open benches in the greenhouse, or under bell jars in the green- 

 house. Chlorine concentrations of 100 and 150 ppm injured or retarded 

 some plants but had no effect on others. Concentrations of 200 and 

 300 ppm always produced some degree of injury to the tops, but had no 



