170 <>N THE PERSPIRATION OF PLANTS. 



the weight of the plant, even in a sunflower, which is the 

 heaviest of plants) ; and tny experiments have so fully an- 

 swered my ideas respecting it, and confirmed my doubts, 

 - without however throwing the least blame on the very per- 

 fect experiments of these excellent botanists, that 1 shall 

 have the greatest pleasure in offering you the result. 

 Doubts re- The constant habit of watching my plants at a very early 



•pecung it. h our i n the morning, and examining them with very power- 

 ful microscopes, had almost convinced me, that the idea of 

 their perspiring was a mistake; still, being acknowledged 

 by such excellent botanists, it required the most absolute 

 conviction, to gain courage to deny a fact so universally re- 

 ceived as a truth. I rise at a very early hour, and had 

 often observed, that, when there was no dew, the leaves re- 

 mained perfectly dry, though examined with a powerful 

 microscope ; that when plants remaiued within doors, they 

 collected dust like any other furniture; and that this dust 

 was to be blown oft' with ease, neither agglutinating nor 

 sticking, which it would do if partially wet: that, after 

 placing a leaf for 4 hours in the opake solar microscope* 

 though it was so placed as to be in its growing state, and 

 was magnified so greatly as to show both species of pores, 

 yet I could never see the smallest quantity of moisture 

 exude, except what I shall now mention, and what I sup- 

 pose may be the insensible perspiration before insisted on. 

 Imensible per- Almost every leaf, if subjected to a large magnifier, ap- 

 spuauon. pears covered with a very fine scurf, which 1 have seen exude 

 as water with the oxigen it is continually giving out, as 

 Jong as the sun shines. In a very short time it turns to a 

 Taken back, jelly; which is, I think, received again into the same pores 

 with the dews of the night; and which I doubt not helps to 

 form that beautiful combination, which changes dead and 

 unorganised matter into living bodies, fitted, as Mirbel 

 beautifully expresses it, for the support of the animal cre- 

 Thi3 very tri- ation. But this is so trifling a perspiration, that it will 

 merely account for the dew, that appears when a vegetable 

 is placed under a glass; but will not raise, or in a very 

 slight degree only, the hygrometer placed within it. 



These doubts suggested the idea of investigating the 

 matter more thoroughly, and I set on foot a number of ex- 

 periments 



fling. 



