146 



The third day it was set in a south window, opon to 

 the full sun. larly in the morning the leaves had at. 

 tained (heir horizontal situation ; by nine o'clock they 

 \vereraisedabove it, and continued so till evening: 

 then they fell to the horizontal situation, and theuce 

 gradually to the usual s'ate of rest. 



The fourth day the plant stood in the same place, 

 but the sun did not appear. The lobes early attained 

 their horizontal situation, but did not rise beyond it, 

 and in the evening closed as usual. 



These rxper nieuts prove, that the whole change is 

 occasioned by light only* To put this beyond dispute, 

 in the evening of the sixth day, the plant was set in a 

 Look. case, on whicn the morning sun shone, the doors 

 standing open. The next day was bright. The lobes 

 which had closed in the evening b^gau to open early in 

 the morning, and by nine o'clock they were raised in 

 the usual manner. I then shut the doors of the book- 

 case : on opening them an hour after, the lobes were 

 all closed as at midnight. Ou opening the doors they 

 opt ni'd again, and in twenty minutes they were fully 

 expanded. This has since been many times repeated, 

 and always with the same success. We can therefore, 

 by admitting or excluding the liiiht, make the plant 

 put on ail is changes. Hence we are certain, that what 

 is called the sle^p of plants, is caused by the absence 

 of light alone, and that their various intermedia instates 

 are owing to its different degrees. 



It has been supposed that the daily motions of the 

 Sensitive plant were likevu.se owing to light arid dark- 

 ness, because it expands itself in the morning, amf 

 closes asain in the evening. From the n-aiu brandies of 

 this plant spring several smaller ones, and from these 

 othcts still less, which support the leaves ranged on 

 <ach side, in pairs over^agiiitiSt one another. Several 

 other plants are of the. same form,. a,id all these close 

 their Icavts in iiu; evening,, and open the.:*ii:i the morn- 

 ing, which therefore is not peculiar to the sensitive 

 plant. But this closes them at any time of the day, if 

 touvhc'd, aoU soon alter opens them agam, You can 



