S88 PHIU)?01'HICAL TRANSACTIONS. [aNNO lUgQ- 



quantity of water had gone off, scarce!)' 20 grains ; though the sand continued 

 moist up to the top till the very last ; the water had imparted a green tincture 

 to the sand, quite to the very top of the tube; and in the phial it had precipi- 

 tated a greenish sediment mixed with black: to the bottom and sides of the 

 tube, as far as it was immersed in the water, adhered pretty much of the green 

 substance described above. 



Q, R, S, &c. are several plants set in phials, ordered in like manner as those 

 above, in October, and the following colder months: these throve not near so 

 much ; nor did the water ascend in near the quantity it did in the hotter sea- 

 sons, when the above trials were made. 



Some Re/lections on the foregoing Experiments. — 1. In plants of the same 

 kind, the less they are in bulk, the smaller the quantity of the fluid mass, in 

 which they are set, is drawn ofF; the wasting of it, where the mass is of equal 

 thickness, being pretty nearly proportioned to the bulk of the plant. Thus, 

 that in the glass marked a, which weighed only 27 grains, drew ofF only 

 2558 grains of the fluid; and that in b, which weighed only 28^, took up but 

 3004 grains, whereas that in h, which weighed 127 grains, spent J4J9O grains 

 of the liquid mass. The water seems to ascend up the vessels of plants in much 

 the same manner as up a filtre: so that as a large filtre draws off more water 

 than a smaller, so a plant that has more and larger vessels takes up a greater 

 share of the fluid, in which it is set, than one that has fewer and smaller ones. 



2. Much the greater part of the fluid mass, that is thus drawn ofl^, and con- 

 veyed into the plants, does not settle or abide there ; but passes through their 

 pores, and is exhaled up into the atmosphere. The least proportion of the 

 water expended, was to the increase of the plant, as 4(3 or 50 to 1 ; and in 

 some the weight of the water drawn off was lOO or 200, nay, in one above 

 700 times as much as the plant had received of addition. This so continual 

 an emission and detachment of water, in so great plenty from the parts of 

 plants, affords a manifest reason why countries that abound with trees, and the 

 especially larger vegetables should be very obnoxious to damps, great humidity 

 in tlieair, and more frequent rains than others that are more open and free. 

 Nor does this moisture go off pure and alone ; but usually carries with it many 

 parts of the same nature with those of the plants through which it passes. The 

 grosser particles indeed are not so easily borne up into the atmosphere, but are 

 usually deposited on the surface of the flowers, leaves, and other parts of the 

 plants. Hence come our mannas, our honies, and other gummous exudations 

 of vegetables : but the finer and lighter parts are with greater ease sent up into 

 the atmosphere ; and thence they are conveyed to our organs of smell, by the 

 air we draw in respiration ; and are pleasant or offensive, beneficial or injurious 



