©N THE PERSPIRATION OF PLANTS. fj* 



that it doubles the weight of the plant, causes the hygro- 

 meter to indicate extreme moisture, and, confined under a Its liquor con- 

 glass, much of its liquor evaporates, condenses on the in- denses<m tnc 

 terior of the glass, and runs down on every side. I have 

 since tried every plant specified as peculiar fir their exces- 

 sive perspiration by Bonnet, Hales, and others, and have 

 found them all loaded with the cryptogamian plant, so 

 that I have not the smallest doubt, that this was by them and has btea 



taken for perspiration ; for what torrents of water would be nmtaken for 

 .1 1. « i , i i perspiration* 



necessary to supply such a transpiration f the air would be 



constantly loaded. The possibility of the mistake any per- 

 son may convince themselves of, and how very likely it was 

 to happen, by taking a pea plant, a sunflower, and a num- 

 ber of other plants unnecessary to mention. 



I said, that leaves had two species of pores ; the first large. Leaves have 

 which are open all the night for the admission of the dew ; two kinds of 

 the second small, from which the oxigen flows. See PI. y, P ° re ' 

 fig. 8, representing part of a leaf sufficiently magnified, to 

 show both # sorts of pores. It is from the smaller that the 

 jelly I have mentioned proceeds; for when the oxigen is sa- 

 turated with moisture, it will naturally give it out in pass- 

 ing these narrow apertures, and this is that scurf which ap<- 

 pears, when the leaves are not covered with a glass ; but 

 which flies upward, and is condensed on the interior, when 

 they are. 



I believe almost every air or gas has moisture, and that a Effect of a 

 full stream of oxigen directed against a glass would cover stream of ox i* 

 it with steam* I have just tried the experiment, and it has S6n " 

 succeeded. It will of course depend upon its being nearly 

 saturated with moisture, or not; and upon the pressure it 

 afterward receives. I have endeavoured to condense my 

 subject as much as possible, without I hope rendering it un-» 

 intelligible. Should I see this in your first publication, it 

 will serve as a hint to give you a farther letter on the forma- 

 tion of the leaf, and the winter bud. The latter certainly 

 is of the first consequence in botany, and may be called the 

 first source of life in the vegetable world. 



Your obliged servant, 



A. IBBETSON. 



HI. 



