136 REMARKS ON GROWING PLANTS IN GLASS CASES. 



that season. In winter, too, when coal fires mostly abound, and gas 

 is most abundantly generated, deciduous plants are protected from its 

 noxious operation by suspension of their vegetating powers ; but the 

 leaves of evergreens, which continue to grow through that season, are 

 constantly exposed to its action, when present in its greatest intensity. 

 Accordingly, in many of the suburban districts around London, espe- 

 cially in the course of the river, where new manufactories are con- 

 stantly rising up, the atmosphere is so highly charged with noxious 

 matters, that many deciduous plants, and almost all evergreens, cease 

 to flourish, or exhibit only a sickly vegetation. 



In an interesting biographical sketch of his late lamented friend* 

 Dr. Turner, Professor Christison confirms, by subsequent experience, 

 the opinion formerly given respecting the noxious operation of the 

 sulphurous and muriatic gases on plants ; he describes their action as 

 so energetic, that, in the course of two days, the whole vegetation of 

 various species of plants may be destroyed by quantities so minute as 

 to be altogether inappreciable by the senses. On two occasions he 

 was able to trace the identical effects of the same kind of works (the 

 black ash manufactory) on the great scale, which his friend and him- 

 self witnessed in their researches. In one instance, the devastation 

 committed was enormous, vegetation being for the most part miserably 

 stunted, or blasted altogether, to a distance of fully a third of a mile 

 from the works, in the prevailing direction of the wind. Against the 

 evils arising from such a vitiated atmosphere, the plan of Mr. Ward 

 provides effectual protection, as the success of his own establish- 

 ment amply demonstrates. 



Condition of Plants, in regard to Water, in close Cases and in the 



free Atmosphere. 



In considering the conditions essential to vegetation, water may be 

 allowed to claim the first place ; for, if the vegetable exists in a state 

 perfectly dry, neither the seed nor the plant can exert that action on 

 the air which is essential for its developemenl and growth. It is 

 11 owing, therefore, to the prevention of the escape of the moisture 

 within the cases, as Mr. Ward observes, that plants will grow in 

 them for iraany months, or even years, without requiring fresh sup- 

 plies of water: thus, the Poa and Nephrodium, above mentioned, 

 grew for four years in the bottle without receiving one drop of fresh 



