58 THE AQUARIUM. 
CHAPTHER-W¥. 
8 MILARITY BETWEEN THE FUNCTIONS OF PLANTS AND ANI- 
MALS —THE AQUARIUM — PRINCIPLES UPON WHICH IT IS 
SUSTAINED—-EARLY EXPERIMENTS WITH THE AQUARIUM— 
PLANTS MOST SUITABLE FOR THE PURPOSE—SEA WEEDS, 
MOULD, LICHENS, MOSSES, FERNS. 
T is a very curious fact that in many of 
the functions of plants, we observe a 
close resemblance to those witnessed in 
animal life; thus, the circulation of the 
sap, which will be more fully described 
hereafter, is in effect precisely similar 
to the circulation of the blood in the human 
body, vessels being provided in each, which 
are peculiarly adapted to carrying the fluids 
which support their existence to the parts 
where they are needed. Respiration is also a point 
in which great similarity exists. Leaves are the 
breathing organs of plants; through them the sap is 
brought into contact with the air, where it absorbs 
that which is necessary for its purification. In this 
operation we shall notice a wonderful provision by 
which nature seeks to preserve a proper balance be- 
tween the requirements of the animal and vegetable 
world In the purification of the blood, the air taken 
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