148 On the effects of the Poisonotis Gases on Vegetables. 



upon general life, which in animals follows so remarkably in- 

 juries inflicted by the purest local irritants.* 



Cyanogen appears allied to the two last gases in property, 

 but is more energetic. Two cubic inches diluted with 230 

 times their volume of air affected a mignonette plant in five 

 hours ; half a cubic inch in 700 volumes of air affected another 

 in twelve hours ; and a third of a cubic inch in 1700 volumes 

 of air, affected another in twenty-four hours. The leaves 

 drooped from the stem without losing colour, and removal into 

 the air, after the drooping began, did not save the plants. 



Carbonic oxide is also probably of the same class, but its 

 power is much inferior. Four cubic inches and a-half diluted 

 with 100 times their volume of air had no effect in twenty-four 

 hours on a mignonette plant. Twenty-three cubic inches, with 

 five times their volume of air, appeared to have as little effect 



• Other occupations prevent us making the requisite inquiries for exa- 

 mining such practical conclusions as our experiments seem to lead to. One, 

 however, may be briefly mentioned. The differences described above show 

 that the injury sustained by vegetation in the heart and vicinity of a great 

 city must be caused by some irritant gas, if circumstances regarding the 

 soil and exposure do not account for it, which they seldom or never will. 

 The plants are rarely killed altogether ; their vegetation is merely blight- 

 ed for the season. In the spring it recommences with a luxuriance not 

 surpassed in country situations ; but when the leaves attain maturity, and 

 have no longer the superabundant supply of moisture they received while 

 young, they are blighted anew. How exactly do these phenomena concur 

 with what we should expect from the influence of the irritating gases as 

 ascertained in our experiments. Such a gas, it is well known, is disenga- 

 ged in abundance from our coal-fires, — namely the sulphurous acid. There 

 has long been a vulgar and very general notion, that coal smoke diffused 

 and diluted in the atmosphere hurts vegetation ; but we are not aware that 

 it has rested till now on any solid reason. A curious fact, indeed, and the 

 only one we have been able to find, is mentioned in Evelyn's Fumifugiumy 

 — namely, that one year, when Newcastle was besieged during the civil 

 war at the Revolution, and coals were in consequence exceedingly scarce in 

 London, in various gardens of the nobility in the metropolis fruit trees, 

 which never bore fruit either before or after, were loaded with it. But the 

 Fumifugium contains so many monstrous and incredible facts, and shows 

 such an uncompromising determination to call in the aid of coal-smoke to 

 account for everything wrong in London which could not be more easily 

 explained, that the modern inquirer will naturally pause before he gives 

 the lively and ingenious author credit even for what appears probable. 



