668 Hygiene of House Plants. [ November, 
A group of plants is so attractive and so interesting in its form 
and development, that we would gladly be sure that its presence 
contributes as much to the health of a room as to its beauty. An 
entirely satisfactory investigation of this matter is scarcely possi- 
ble, for analyses of air, careful experiments, and observations re- 
lating to the influence of plants growing in occupied rooms, are 
for the most part wholly wanting. The general effect of vege- 
tation in the economy of nature is too wel known to be dwelt 
upon here. Most are familiar with the fact that animals are de- 
pendent upon plants for food, and that after growth, reproduc- 
tion, and death, the materials of animal structure return to the 
vegetable, and thus everywhere, in ever-recurring cycles, the 
dead animal returns to life in the plant ; everywhere, for vegeta- 
ble life is everywhere, rooted in earth, floating in water, buoyed 
in air, and everywhere attractive, varied, and interesting. What 
is said in regard to plant life and growth in this article refers 
only to the higher and flowering plants. Such plants often remove 
much from both the earth and the air in which they grow, and 
in return they give much to the air; but while living they return 
almost nothing to the earth, only now and then a stray leaf or 
bit of bratich. Hence, growing plants tend to change the nature 
of both soil and air. The chief processes of plant life, absorb- 
ing, assimilating, exhaling, are carried on with immense energy: 
How great these forces are we do not yet know, but exper- 
ments, such as those of President Clark, of Amherst, have lately 
been made, which have given us glimpses of the power exerted in 
vegetable growth. Without direct proof of the fact few would 
be ready to believe that the outward pressure of sap in a hegre 
could ever equal that of a column of water over eighty feet high ; 
that even in a bit of root wholly severed from the tree, though 
of course only recently cut off, the force of the sap-pressure c° ld 
be as great, or that in a squash-vine it could equal that of a col- 
umn of water nearly fifty feet high. No one, I think, would 
have supposed that a growing squash in its efforts to increase, 
would, when confined, lift a weight which was gradually 1 
creased to one ton, then to two tons, and finally to two tons and 
a half. These experiments are so well known that an account 0 
them is unnecessary here, but they tell us very much of i 
forces acting in vegetation, which are so silent and impereeptib le 
that we too often fail to notice them. In every field of growing 
grain chemical changes are taking place such as no chemist can 
produce ; forces are in action which, if so directed, could heave — 
