SECT. II. GASES. 51 



space of three days, when put into the exhausted 

 receiver of an air-pump whether in the shade or the 

 sun. But plants with thick and succulent leaves 

 seem capable of supporting vegetation in vacuo, at 

 least if exposed to the sun. A plant of the Cactus 

 Opuntia lived more than a month in this state 

 without showing any symptoms of decay, except 

 that the epidermis seemed dry, which again reco- 

 vered its freshness, however, in the atmospheric 

 air.* And though plants with thin leaves gene- 

 rally died under the experiment, yet there were 

 exceptions even among them. A plant of the Po~ 

 tygonum Persicaria lived for six months in the 

 vacuum of an air-pump, and was at the end of the 

 experiment as fresh and vigorous as at the be- 

 ginning, with the exception of two or three leaves 

 near the root, which were withered. The same was 

 the case also with plants of the Epilobium molle, 

 Epilobium hirsutum, Ly thrum Salicaria, and Inula 

 dy sent erica. They were placed in the light, but not 

 so as to receive the direct rays of the sun ; to which 

 when they were exposed they withered, even though 

 the rays were but feeble. 



It has been said indeed that roses will remain 

 longer fresh in vacuo than in common air. But 

 this is a mistake. In the latter case the petals, no 

 doubt, fall sooner; but this is merely the natural 

 effect of vegetation, and not a symptom of decom- 

 position or decay, as is proved from the inspection 

 * Sur la Veg. chap. vi. sect. v. 

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