312 
PECULIARITIES OF PLANTS. 
their thirst. Still we can scarcely suppose this to be their destined 
use, for many other trees bear similar appendages, which could not 
be readily if at all emptied. Besides, the situation in which some 
of them grow, would render such a providential provision unneces¬ 
sary. Whatever be their uses, there can be no doubt but they are 
necessary to the welfare and growth of the plant; for if one be inad¬ 
vertently injured, the leaf to which it was attached becomes sickly, 
and for the most part incapable of performing its natural functions. 
38 
So great a quantity of spiral vessels was discovered by Mr. Valen¬ 
tine, in the stem and petioles, that no plant has yet been noticed in 
which they are equally abundant. Now Bischoff ascertained that 
the air conveyed by spiral vessels contains about 28 per cent, of 
Oxygen, and as an excessive supply of Oxygen is destructive of ve¬ 
getable life, it has been suggested, that the pitchers are intended to 
rid the plant of its oxygen, and that the water they contain has been 
discharged by the spiral vessels themselves. An observation of the 
late Dr. Jack appears to favour this opinion, for on examining the 
