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are diminishing the oxygen in the air, so necessary for them, and increasing the 
amount of carbonic acid, so injurious to them; or, rather, which would be so in- 
jurious if it were allowed to accumulate ; the reason why it does not, is because 
plants consume it as soon as formed. Chemical experiments have shewn that, 
when the leaves and green parts of plants are exposed to sunlight, they possess 
the wonderful power of decomposing the carbonic acid of the atmosphere It 
is absorbed through the stomata, ana the delicate cells are the chambers of the 
laboratory where it is decomposed, and the whole of its carbon is taken by the 
plant and assimilated with the water and other matters collected from the soil 
and air to form cellulose, which becomes wood, pulp, starch, sugar, etc., etc., 
according to circumstances, while the whole of the oxygen it contained is 
evolved back again into the air because useless to the plant, the full amount 
required by it to complete the composition of cellulose already existing there 
as one of the constituents of water. This is proved by the fact that there is a 
constant relation between the amount of carbonic acid gas absorbed and the oxygen 
exhaled. While the plant is a true apparatus of reduction, the animal is a true 
apparatus ef combustion, in which the substances it derives from the vegetable 
are burnt and restored to the atmosphere in the form of carbonic acid, water and 
ammonia, ready to be again absorbed by the plant and to re-pass through the phases 
of organic life. The important influences exercised by vegetation on nature 
will be at once appreciated when it is remembered that this is the only known 
process by which oxygen gas, so essential to our existence, 1s restored to the 
atmosphere ina free condition. Thus we see that the two great organized king- 
doms of nature are made to co-operate in the execution of the same design ; each 
ministering to the other and preserving thal one balance in the constitution of the 
atmosphere which adapts it to the welfare and activity of every order of being, 
and which would soon be destroyed were the operations of either of them to be 
suspended. It is impossible to contemplate so special an adjustment of opposite 
effects without admiring this beautiful dispensation of Providence, extending 
over so vast a scale of being, and demonstrating the unity of plan upon which 
the whole system of organized creation has been devised. 
The last object of our collection is the stone. To anyone who has never 
examined a stone critically, it would appear to bea perfectly homogeneous mass, 
with no structure at all. This is seldom the case, however, Almost every. solid, 
when slowly deposited froma liquid or aériform condition, assumes a definite 
symmetrical shape, called a crystal. ‘The perfect crystal represents the natural 
condition of a substance, and the form peculiar to each is one of its most impor- 
tant characteristics. The idea of symmetry is inherent in every human mind, 
it may be more or less cultivated by experience ; but the germs of the idea are 
found in the most untutored. However rude his condition, man is pleased with 
asymmetrical arrangement of objects, and his mind is offended when his eye 
detects a violation of the laws of symmetry, although he may have no name for 
the idea. Corresponding with this idea, we find symmetry everywhere in nature, 
The parts of fan animal are most symmetrically arranged round the body, as also 
