On the Source ef Nutrition tnfucculent Vegetables, 3 



office of fo many receptacles of fap fufficicnt to anfwcr the demands of thefe trying feafons ; 

 and which are recruited in a greater or lefs degree by every (hower. Thefe magazines of 

 food are emptied in the flowering feafon, probably to feed the expanding capfules,; for by the 

 time the feeds are ripe, the plants are exhaufted, and fufFer what may be called a vegetable 

 death, by a natural proccfs. 



Experiment 2. The fempervivum teilorum, which refembles the fedums in habit, alfo 

 agrees with them in the property in queftion : for an offset of fempervivum, of the weight of 

 250 grains, being left in a window from the 29th of April to the third of June, loft 116 

 grains, and appeared to be in a very exhaufted condition, but its faculty to vegetate remained 

 unimpaired ; for the fame offset was afterwards placed for an hour every other day in a glafs 

 of rain-water to the end of the month, by which it was fo much recruited, as to produce a 

 new (hoot, and the joint weight of parent and offspring amounted to 170 grains, Notwith- 

 ftanding the conclufive refult of the two laft experiments, it may, perhaps, be alleged, that 

 the dry air of a chamber does not give fucculent plants that opportunity to procure water which 

 the atmofphere affords them during fair weather, efpccially in the nights, when the dews arc 

 formed : but this objeflion feems to be overturned by the fucceeding paragraph. 



Experiment 3. I fufpended diff*erent offsets of fempervivum tedorum in glafs-bells, having 

 their mouths placed in water; which did not rife in the yefllls far enough to touch the plant. 

 The air which furrounded the offsets was kept fo moift by this fort of confinement that the in- 

 lidcs of the jars appeared conftantly covered with vapour : at the fame time care was taken 

 not to expofe the apparatus to the dlre£l rays of the fun. A plant treated in this manner in 

 June, loft a fixth part of its weight in a fortnight. Another plant, fubje£ted to a fimilar trial 

 during the two laft weeks of September, loft but t't P^rt of its weight. The lofs of fubftance 

 which is here remarked, will be beft explained by the following fail. — Dew does not form 

 with equal facility on all kinds of bodies ; efpecially in a temperature of 50°, or higher : for 

 inftance, glafs colledls dew from air, which is not in a ftate to impart the fame to varniflied 

 wood or poliflied metals ; and were we to form a fcale of thefe affinities by experiment, green 

 vegetables would take their refpe6tive ftations, fomewhere between glafs and fome one of the 

 metals ; becaufe, when the three fubftances in queftion are expofed to the open air, glafs is 

 covered with dew in the firft place ; and the vapour fixes on clean metallic furfaces, after the 

 leaves of living fhrubs. On this account, the water contained by the air ufed in the laft ex- 

 periment, attached itfelf to the fides of the jars, in preference to the offsets of fempervivum; 

 which being deprived of dew, could not repair the Icfs they fufFered by evaporation for want 

 of aqueous particles in a condenfed form. The uniform refult of the preceding experiments 

 feems to prove, beyond a poflibility of doubt, that the fucculent vegetables of Europe receive 

 their portion of nutrition by the common vehicle of water conveyed to them in the common 

 way by the earth, or depofited on their leaves in the form of rain; and I have reafon to fup- 

 pofe that plants of the fame defcription, natives of tropical countries, are regulated by the fame 

 principle of economy; for a plant of aloe perfoliata, which was fufpended for 52 days, about 

 the conclufion of autumn, in a room with a northern afpeft, loft fomething more than one- 

 fourth of its weight in this dry fituation; but no attempts were made to repair the lofs by the 

 methods purfued in the firft experiment. 



B 2 Defcription 



