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' Both these species are natives of Brazil, and, in their 
proper habitation grow to the height of seven or eight 
feet. Dr. Darwin accounts for what is called the sleep 
of the plant, by the absence of the stimulus of light; 
but more recent observations have disproved this con¬ 
jecture, as the leaves are found to contract by five or six 
o’clock in the longest summer days, when the sun 
remains above the horizon some hours longer; nor do 
they continue shut till he rises, as they are often fully 
expanded at the first break of dawn. Their suscepti¬ 
bility also varies greatly according to the degree of 
temperature in which they are placed; when kept in a 
warm stove, the smallest drop of water falling on their 
leaves, nay, even a passing breath, will cause them 
instantly to collapse. As it is this peculiarity which 
gives the plant its chief value, it is, of course, generally 
placed in such a temperature as will be likely to keep 
this sensitive character in full vigour. There are many 
uninjured from contact with any other body. This property has given 
rise to a conjecture, that plants not only are furnished with a set of vessels 
similar to our veins and arteries, but may also have what answers to the 
nervous system in animals; and experiments have been made to prove 
this, by subjecting plants to the action of certain vegetable poisons known 
to destroy animal life, by affecting the nervous system alone. The result 
was, the leaves soon presented a withered appearance, which was followed, 
in a short time, by the death of the plant 
