I 



the Poisonous Gases o?i Vegetables, 143 



the plants were distinctly acted on. The tips of some of the 

 mignonette leaves and larch leaves were grayish-coloured, 

 shrivelled, and dry-looking, and the three lower leaves of the la- 

 burnum were speckled with irregular grayish-yellow dry-looking . 

 spots. The air was then renewed, together with the same 

 proportion of gas, and it was allowed to act for forty-eight 

 hours longer, during which the effects slowly extended to- 

 "wards the footstalks and over more of the leaves. The plants 

 were then taken out. The earth continued moist. The 

 middle leaves of th'e mignonette, but the lower leaves of both 

 the larch and the laburnum had suffered most. The leaves 

 of the mignonette were withered chiefly at the tips or edges ; — 

 most of those of the larch at the tips, in some, however, at 

 the middle ; — those of the laburnum were affected more uni- 

 formly over their whole disk, they drooped considerably, a 

 gentle touch was sufficient to break the leaflets from the foot- 

 stalks, and the footstalks from the stem, — nay, some of the 

 leaflets had dropped off while the plant was in the jar. The 

 bud-leaves were not injured in any of the plants. 



* The effect of this poison seemed to resemble considerably 

 the ordinary decay of the leaves in autumn. It was invari- 

 ably produced in several repetitions of the foregoing expe- 

 riment. — The proportion of gas was sometimes a ten-thou- 

 sandth only, the quantity a fifth of a cubic inch, and yet the 

 whole unfolded leaves were nearly destroyed in forty-eight 

 hours. We remarked that the withering and curling of the 

 leaves always rapidly increased for an hour or two after the 

 removal of the plants into the open air, so that some leaves 

 which had been apparently but little affected in the jar died 

 afterwards in the air quickly and completely. The whole 

 plant, however, was never killed by these small proportions. 

 Segments near the footstalks, particularly of the upper leaves, 

 continued green and juicy, and the buds put forth fresh 

 though generally stunted leaves. Even when the proportion 

 of gas was larger, the plants were not killed altogether : the 

 stem was not affected unless the proportion was considerable, 

 and even then it was only the top which suffered. — It will be 

 afterwards seen how different these phenomena are from the 

 effects of deleterious gases not irritants. 



