160 EFFECTS OF GASES ON PLANTS. 



organisation; others as narcotic poisons, inducing a drooping and 

 decay of the entire plant. To the former class belong sulphurous 

 acid gas, hydrochloric acid gas, chlorine and nitrous acid gas ; while 

 amongst the latter are included sulphuretted hydrogen, cyanogen, 

 carbonic oxide, and ammonia. 



Sulphurous Acid Gas is highly injurious to plants. It pro- 

 duces greyish-yellow dry-looking spots on the leaves, which gradually 

 extend until the leaves are destroyed. The effect resembles much 

 the ordinary decay of the leaves in autumn. The proportion of 

 gas, in some experiments, was only 1 in 9000 or 10,000 parts of air, 

 and the quantity i of a cubic inch ; and yet the whole unfolded 

 leaves of a mignonette plant were destroyed in forty-eight hours. 

 This proportion of the gas is hardly or iiot at aU discoverable by the 

 smell. 



Hydrochloric Acid Gas produces effects . similar and scarcely 

 inferior to those of the last-mentioned gas. When i of a cubic inch 

 is diluted with 10,000 parts of air, it acts destructively on Laburnum 

 and Larch, destroying the whole vegetation in less than two days. 

 Even when in quantity not perceptible by the smell, it still acts as an 

 irritant poison. 



Sulphuretted Hydrogen acts in a different way from the acid 

 gases. The latter attack the leaves at the tips first, and gradually 

 extend their operation to the leaf-stalks. When in considerable 

 proportion, their effects begin in a few minutes ; and, if diluted, the 

 parts not attacked generally survive if the plants are removed iato 

 the air. But in the case of sulphuretted hydrogen, the leaves, without 

 being injured in texture or colour, become flaccid and drooping, and 

 the plant does not recover when removed into the air. It requires a 

 larger quantity of this gas to produce the effects stated. When six 

 cubic inches are added to sixty times their volume of air, the droop- 

 ing begins in ten hours. This gas then acts like a narcotic poison, 

 by destroying life throughout the whole plant at once. 



These observations point out the great injury which is caused to 

 plants by the gases given off during the combustion of coal, and more 

 especially by certain chemical works. In the vicinity of the latter, 

 the vegetation, for a considerable distance around, is often destroyed, 

 ■ particularly in the direction of the prevailing winds of the locality. 

 The atmosphere of large manufacturing towns, in which fuliginous 

 matter and sulphurous gases abound, is peculiarly hurtful to vegetable 

 life. In order to protect plants from such prejudicial influences, Mr. 

 N. B. Ward has invented close glass cases, in which plants can be 

 grown independently of the noxious atmosphere around. These 

 cases consist of a trough containing soil, and a frame of glass, which 

 is accurately fitted upon it. The soil is well supplied with water at 

 first, and after the plants are put in, they are kept exposed to the 



