3j C Z OS THE SUPPOSED PERSPIRATION OF PLANTS. 



plant*. I have also seen the beginning of the hairs of the 



leaf taken for it. 



J*o perspiration Jft the three or four years that I have been (as lorn? as 

 Visible with a .. ' , , . , * , ,. . .. 



*ery high mag- tne leaves last) endeavouring to discover perspiration, it 



aifyingpower. appears to me impossible I should not have found it, if it 

 did exist : but I have sought it with microscopes that mag- 

 nified .so extremely, as to preveut my being deceived by 

 other objects. I regret indeed the little use made of au 

 instrument now carried to a degree of perfection, which 

 must daily bring new wonders to our admiring senses. With 

 respect to perspiration, it \s so little shown, though the 

 smallest hairs of the leaf are enlarged to the size of a ruler, 

 and the water is seen running up as the rarefaction of the 

 air forces it from the increased vrarmth of the glass. Nay, 

 the pores of the leaf are so enlarged, that an object five 

 times as small could be seen and examined: why then should 

 I not see moisture, if it existed? 



In my former papers (.which were written a long time 

 since,) I did not mention (because I was not fully aware of 

 it) the very defective manner made use of to try the quantity 

 of perspiration given by plants, and to evince its existence, 

 till the desire of studying the effect of various degrees of 

 heat on plants, made me a constant attendant on the hot- 

 Heat increases house, green house, hot walls, and glasses, &c. I then 

 m£a planu^on ^ oun{ ^? * nat an y increase of heat helped greatly to increase 

 leaves, the number of cryptogamian plants on those leaves, on which 



mturaUecre- " tne ^ were no * a * a ^ inclined to grow ; and that, beside this, 

 tions. they produced secretions unknown to the plant in its na- 



Themelon. tural situation. The melon gives a very curious one, found 

 on the edge of the leaf of the plant every morning : but, 

 instead of covering the plant from all air, leave £1 a little by 

 raising the glass, and the moisture intirely ceases. It is the 

 The cucumber. sarae 5 though not so much, with the cucumber. There is 

 not the smallest appearance of moisture without the plant 

 is first rendered ill, to study its secretions. It is objected 

 to me, that I left the plant so long (being three hours) that 



* See Plate IX, Figs. 15, and 1C, the cryptogamian plant on the 

 mimulus, or monkey flower : tig. 17, those on the pea, which are 

 recumbent: fig. 18, those on the sunflower. They seldom appear 

 on young leaves, or on any leaf, till the plant is near flowering. 



the 



