25* EXPERIMENTS ON HEMP. 



ting the sun and air to the parts within ; whereas many 

 of them not only dose their petals at night, but also de- 

 five additional protection from the green leaves of the 

 plant folding closely about them. Convolvulus arve?!- 

 sis, t. 312, AnagalUs arvensis, t. 529, Calendula pluvi- 

 alis, and many others, are well known to shut up their 

 flowers against the approach of rain ; whence the 

 Anagallis has been called the Poor Man's Weather- 

 glass. It has been observed bv Linnaeus that flowers 

 lose this fine sensibility, either after the anthers have 

 performed their oflTicc, or when deprived of them arti- 

 ficially ; nor do I doubt the fact. I have had reason 

 to think that, during a long continuance of wet, the sen- 

 sibility of the Anagallis is sometimes exhausted ; and it 

 is evident that very sudden thunder-showers often take 

 such flo\vers by surprise, the previous state of the atmos- 

 phere not having been such as to give them due warning. 

 That parts of vegetables not only lose their irritabili- 

 ty, but even their vital principle, in consequence of hav- 

 ing accomplished the ends of their being, appears from 

 an experiment of Linnceus upon Hemp. This is a dioe- 

 cious plant, see/?. 241, and Linnaeus kept several fer- 

 tile-flowered individuals in separate apartments from tfie 

 barren ones, in order to try whether they could perfect 

 their seeds without the aid of pollen. Some few how- 

 ever remained with the barren-flowered plants, and these 

 ripened seed in due time, their stigmas having faded and 

 withered soon after they had received the pollen. On 

 the contrary, the stigmas which had been out of its 

 reach continued green and vigorous, as if in vain expec- 

 tation, nor did they begin to fade till they had thus last- 



