tion-hose
into the same region, and their spongioles are so effectually closed
by this process, that they can no longer perform their office, and the
plant that bears them dies. Plants whose roots ramify among the roots
of poppies become unwilling opium-eaters, from the exudation of this
narcotic principle into the ground, and are stunted, like the children
of Gin Lane.

The Aquarium furnishes a very interesting example of the mutual
dependence of the three natural kingdoms. Here, in a box holding a few
gallons of water and a little atmospheric air, is a miniature world,
secluded, and supplying its own wants. Its success depends on the number
and character of the animals and plants being so adapted as to secure
just the requisite amount of active growth to each to sustain the life
of the other: that the plants should be sufficient to support, by the
superfluities of their growth, the vegetarians among the animated tribes
that surround them; and that all the animal tribes of the aquarium,
whether subsisting upon the vegetables or on their smaller and weaker
fellow-creatures, should restore to the water in excrements the mineral
substances which will enable the plants to make good the daily loss
occasioned by the depredations of the sea-rovers that live upon them.
Thus an aquarium, its constituents once correctly adjusted, has all the
requisites for perpetuity; or rather, the only obstacle to its unlimited
continuance is, that it is a mortal, and not a Divine hand, that
controls its light and heat.

In the examination of the materials appropriated by plants from the
soil, we find that mineral substances are sometimes taken up in solution
in larger amount than the growth of the plant and the maturation of its
fruit require, and the excess is deposited again, in crystalline form
in the substance of the plant. If we cut across a stalk of the
garden rhubarb, we can see, with the aid of a microscope, the fine
needle-shaped crystals of oxalate of potash lying among the fibres of
the plant,--a provision for an extra supply of the oxalic acid which is
the source of the intense sourness of this vegetable. When the sap of
the sugar-maple is boiled down to the consistence of syrup and allowed
to stand, it sometimes deposits a considerable amount of sand; indeed,
this is probably always present in some degree, and justifies, perhaps,
the occasional complaint of the grittiness of maple-sugar. But it is a
native grit, and not chargea