EXPERIMENTS ON HEMP. 251 



from the green leaves of the plant folding closely about 

 them. Convolvulus arvensis, t. 312, Anagallis ar- 

 vensis, t. 529, Calendula plwoialis, 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 by Linnaeus that flowers lose this fine sen- 

 sibility, eitlier after the anthers have performed their 

 office, or when deprived of them artificially ; nor do 

 I doubt the fact. I have had reason to think that, 

 during a long continuance of wet, the sensibility of 

 the Anagallis is sometimes exhausted ; and it is evi- 

 dent that veiy sudden thunder-showers often take 

 such flowers by surprise, the previous state of the at- 

 mosphere not having been such as to give them due 



warning. 



o 



That parts of vegetables not only lose their irrita- 

 bility, but even their vital principle, in consequence of 

 having accomplished the ends of their being, appears 

 from an experiment of Linneeus upon Hemp. This 

 is a dioecious plant, see p. 234, and Linnasus kept 

 several fertile-flowered individuals in separate apart- 

 ments from the barren ones, in order to try whether 

 they could perfect their seeds without the aid of pol- 

 len. Some few however 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 



