THE AQUATIC PLANT CASE, OR PARLOUR AQUARIUM. 
may so term it, a small plant of the Vallisneria spiralis was introduced, its roots being inserted in the 
mud and sand, and covered by one of the loose stones so as to retain the plant in its position. The 
Vallisneria spiralis is one of those delicate aquatic plants generally selected by the microscopist for 
the exhibition of the circulation of the sap in plants; it throws out an abundance of long strap-shaped 
leaves of about a quarter of an inch in breadth, and from one to three feet in length. These leaves, 
when the sun shines on them, evolve a continued stream of oxygen gas, which rises in a current of 
minute bubbles, particularly from any part of the leaf which may have received an injury. 
“ The materials being thus arranged, all appeared to go on well for a short time, until circumstances 
occurred which indicated that another and very material agent was required to perfect the adjustment, 
and which, from my not having thought of it at the time of commencing the experiment, had not been 
provided against. The circumstances I allude to, arose from the decay of the leaves of the Vallisneria, 
which became yellow from having lost their vitality, and began to decompose. This, by accumulation, 
rendered the water turbid, and caused a growth of mucous or green slimy matter on the surface of the 
water, and on the sides of the receiver. If this had been allowed to increase, I conceive that the health 
of the fish must have suffered, and probably their vital functions have been destroyed. The removal of 
these decaying leaves from the water, therefore, became a point of paramount importance; and to effect 
this, I had recourse to a very useful little scavenger, whose beneficial functions have been too much 
overlooked in the economy of animal life; I mean the water snail, whose natural food is the veiy 
green slimy growth or mucus and decaying vegetable matter, which threatened to destroy the object 
which was wished to be obtained. Five or six of these creatures—the Limncea stagnalis —were conse¬ 
quently introduced, and by their continued and rapid locomotion, and extraordinary voracity, they 
soon removed the cause of interference and restored the whole to a healthy state; thus perfecting the 
balance between the animal and vegetable inhabitants, and enabling both to perform their functions 
with health and energy. 
“ So luxuriant was the growth of the Vallisneria under these circumstances, that by the autumn 
the one solitary plant that had been originally introduced had thrown out very numerous offshoots and 
suckers, thus multiplying to the extent of upwards of thirty-five strong plants, and these threw up 
their long spiral flower stems in all directions, so that, at one time, more than forty blossoms were 
counted lying on the surface of the water. 
“ The fish have been lively, bright in colour, and appear very healthy; and the snails also, judging 
from the enormous quantity of gelatinous masses of eggs which they have deposited on all parts of the 
receiver, as well as on the fragments of stone—appear to thrive wonderfully, and besides their functions 
in sustaining the perfect adjustment of the series, afford a large quantity of food to the fish in the form 
of the young snails, which are devoured as soon as they exhibit signs of vitality and locomotion, and 
before their shell has become hardened. 
“ Thus we have that admirable balance sustained between the animal and vegetable kingdoms, and 
that in a liquid element. The fish in its respiration consumes the oxygen held in solution by the 
water as atmospheric air, furnishes carbonic acid, feeds on the insects and young snails, and excretes 
material well adapted as a rich food to the plant, and well fitted for its luxuriant growth. The plant 
by its respiration consumes the carbonic acid produced by the fish, appropriating the carbon to the 
construction of its tissues and fibres, and liberates the oxygen in its gaseous state to sustain the healthy 
functions of the animal life, at the same time that it feeds on the rejected matter which has fulfilled 
its purposes in the nourishment of the fish and snail, and preserves the water constantly in a clean 
and healthy condition. While the slimy snail, finding its proper nutriment in the decomposing vege¬ 
table matter and minute confervoid growth, prevents their accumulation by removing them, and by its 
vital powers converts what would otherwise act as a poison into a rich and fruitful nutriment, again to 
constitute a pabulum for the vegetable growth, while it also acts the important part of a purveyor 
to its finny neighbours.” 
In this way is the economy of the animal and vegetable kingdoms wisely and beneficently adjusted 
so that the vital functions of each are permanently maintained. 
