a On the Source of Nuiritlen infucculint Vegetables, 



animals, wh6fe opportunities to procure food are precarious. Now as fucculent plants are 

 intended to grow on rocks, and in other dry fituations, where their fupplies of humidity fufFer 

 frequent and long interruptions, in all probability they bear the fame relation to the vegetable 

 tribes, which reptiles bear to other animated beings. 



The queftion whether of the two opinions now dated is true, will be beft refolved by a fet 

 ef ftatical experiments, made with fucculent plants furrounded by dry air. Should they ap- 

 pear to gain weight when treated in this manner, the former notion muft be adopted; but 

 fliould they happen to lofe part of their fubllancc, the latter will have the preference : for the 

 aft of vegetating implies the growth of parts already formed, and the production of new or- 

 gans to complete the plant. The following experiments were made, in order to decide the 

 queftion under confideration ; which I fijall now relate without further apology. 



Experiment I*. Three plants of fedum acre, weighing 69I grains, were fufpended in a 

 proper manner before a window, on the 6th of September, 1790: being again examined on 

 the 25th of the fame month, their weight was reduced to 42 grains- They were then placed 

 in water for 24 hours, and afterwards expofed to the light and air for half that period, to give 

 the water adhering to the plants an opportunity to evaporate. At the end of this time, their 

 weio-ht was 631 grains; which is 6^ grains lefs than their original weight. Perhaps the pre- 

 ceding deficiency is owing in part to the plants not being weighed before part of their fap was 

 loft together with the fuperfluous water ; but the following circumftance (hould alfo be taken 

 into the account. If a glafs of limewater be placed under a glafs jar containing a plant of 

 fedum, the lime will be precipitated in the courfe of three or four days; from which we may 

 conclude with reafon, that part of the carbon of the plant is converted, in all fimilar cafes, into 

 gas by the oxygen of the atmofphere. The fame experiment being repeated with fedum re- 

 flexum, as well as fedum acre, a confiderable lofs of weight took place in both trials ; and I 

 think the tendency and uniformity of the refult will juftify the fucceeding remarks and con- 



cluHons. 



The fedum acre, in all probability, draws no more nutriment from the air than other plants; 

 at the fame time, the herb in queftion, as well as the reft of the fucculent tribe, can evidently 

 retain life for an unufual length of time, in fituations incapable of affording them nutrition in 

 the common way. The vegetative principle even continues to act in the fedum, when fuf- 

 pended by the roots, apparently with a view to its prefervation ; for the branches of the plants 

 ufed for the experiment curled, by turning their tips, contrary to the general habit of vegetables, 

 from the window : by this provident fingularity, much light was avoided, and with it an un- 

 neceffary expenditure of fap. The roots in the mean time produced a number of fine fila- 

 ments, as if in fearch of humidity; for they feemed, in this inftance, to imitate trees growing 

 on old buildings, which have been known to connect themfelves with the ground, by means 

 of roots defcending along the fides of the walls. This peculiarity in the conftitutions of the 

 fedums is abfolutely neceflary to their exiftenee ; for thefe plants being intended to grow upon 

 rocks and walls but flightly covered with earths, would be burned up and deftroyed by the 

 droughts of fummcr, but their many fucculent leaves obviate the difafter, by performing the 



• The fubftance of thi» experiment is inferted in Wither. Bot. Arrangement, edit. 3d. Vide art. Sedum. 



oi£ce 



