1202 ARUM. [CLASS XXI. ORDER VII. 
the fruit, by which it is best distinguished as a species, is without or 
only with the rudiments of spines near the base, and the style is 
short, mucronate, slightly curved. 
Habitat.—Ditches in the East and Southern parts of England. 
Perennial; flowering in September. 
These humbie looking plants, like many other of the aquatic 
vegetables, are not known to possess any particular virtues as food or 
medicine; but they are, nevertheless, of great utility. The roots 
growing in the decaying remains of plants in the bottom of the water 
in which they are submersed, absorb abundantly the carbonic acid 
gas as itis formed by these decaying vegetable matters. Carbonic 
acid gas is composed of one atom or one part of oxygen, and one 
atom of carbon, united together; this, as it is circulated through 
the plant, is decomposed by the light, aided probably by the 
vital action of the plant itself. The carbon is applied to the forma- 
tion of the structure of the plant, and the oxygen gas is set free, and 
escapes through the pores or stomata of the cuticle. The gas thus set 
free often accumulates amongst the matted stems and leaves of 
aquatic plants, and if they are agitated by a stick, it is seen to escape 
in large bubbles through the water into the air, and becomes a com- 
ponent part of the atmosphere, and assists in supplying the animal 
creation with gas so necessary for their existence. Thus we find 
that these humble denizons of our ditches and pools perform not only 
when living, but by their decay when dead, a most important office in 
the harmony of the creation. A very simple experiment will prove 
the separation of oxygen gas from water containing carbonic acid 
gas in solution. Take a glass globe or receiver, filled with water 
containing carbonic acid gas in solution, put into it a branch of mint, 
or any other plant fastened by its stem to a plate with a little wax 
and thread, invert the glass full of the water, and place them in the rays 
of the sun, and it will shortly be seen that bubbles of gas escape from 
the leaves and pass to the top of the glass: this gas will be found to 
be oxygen ; and as long as there is any carbonic acid gas in the 
water this process goes on; but in water not containing any carbonic 
acid in solution no change takes place in the plant, nor does any gas 
pass from its leaves. 
GENUS XVIII. A’RUM.—Linn. Cuckow-pint. 
Nat. Ord. Anoi'pEx. Juss. 
Grn. Cuan. Spatha of one leaf, convolute at the base, and enclosing 
aspadix. Spadix with the ovaries inserted at the base, about 
the middle are numerous rows of sessile anthers, and above it is 
naked. Fruit a berry, one celled, many seeded.Name formerly 
written aron, supposed to be an ancient Egyptian word, by 
which the A. colocasia was known, 
