106 



ON THE AQUEOUS EMANATION OF VASCULAR VEGETABLES. 



the receiver with the plant. Duhamel observes, however, that these exhaled 

 waters corrupt sooner than the common water ; and Senebier is assured from 

 analysis, that in fact the water exhaled by vegetables is not perfectly pure. 

 Having placed different plants in a vessel, and collected the water which they 

 exhaled, he found in it a portion foreign to the water : in 11.520 parts of the 

 water exhaled by the vine, he detected 1.25000 of foreign matter. This analysed, 

 appeared to contain a little gummy and a little resinous matter, and the residue, 

 which was neither soluble in water or alcohol, was supposed to be a mixture of 

 lime, and sulphate of lime. Thus not only one third of the water absorbed by the 

 plant remains in its tissue, but nearly the whole of the substances dissolved in the 

 absorbed water, do not escape with the water exhaled, but remain in the 

 vegetable. 



We here perceive, in a manner sufficiently clear, one of the sources of nutrition. 

 The water absorbed by the roots, arrives charged with the substances dissolved 

 in it ; it deposits them in the vegetable, and a portion of the water itself remains 

 with these substances, the rest escapes in the form of water, and nearly in the 

 same state of purity as distilled water. 



Hedwig has compared this evacuation of water to the evacuation of the 

 excrements of animals, and it is in this sense that he says, plants have their liquid 

 excrements. Hales has compared this phenomenon to the insensible perspiration 

 of animals, with which, indeed, exhalation has evident relations, particularly as 

 to the nature of the substance exhaled, and to the manner of exhalation. Both 

 the opinions of Hedwig and Hales appear to me correct, and if I were inclined to 

 pursue the comparison of the two kingdoms, I should willingly admit that the 

 exhalation of vegetables, represents at the same time the evacuation of the excre- 

 ments, and that of the insensible perspiration of animals. It is for this reason 

 that I designate it by a specific name. 



The connexion with this last function is still perceptible in another point of 

 view ; thus, it happens sometimes, that the transpiration of vegetables, when it is 

 very abundant in a given place, becomes visible like perspiration in the form of 

 small drops. It is thus, that drops of water are frequently observed, which are 

 formed on the summit of the leaves of corn, and of many other graminaceous 

 plants on receiving the first rays of the sun. These small drops are also perceived 

 on the serratures of certain plants ; they are arranged with regularity on the 

 leaves of the monk's-hood. It was thought formerly that these small drops of 

 water, very visible at sunrise, were deposited there by the dew ; but Mussenbroeck 

 was the first to ascertain, that they were found also on plants which were sheltered 

 from it, and that they must be attributed to the action of the living vegetable. 

 Must these facts be attributed to exhalation ? Must this water be considered as 

 a true excretion, or rather as the water which exudes from the extremity of the 

 leaves of certain arums, or from the summit of the spathes of the palms — or 

 should they be considered similar to the exuding of the tears of the vine I It 

 would be useful to institute some new observations on this subject. 



