64 ORCHIDS. 
sex in their flowers, they rise to the height of their stature, and 
foreshadow the third great function of animal life,—that of repro- 
duction. Of the whole plant, the flower is the part nearest akin to 
us. Like us, it breathes oxygen, and gives out carbonic acid. Like 
us, it therefore gives out heat; for the flower is the warmest part 
of the plant. Like us, it has rest,—seasons of sleep, so called; 
and for reproduction needs to hoard, and in the process exhausts 
vitality. Like animals, too, plants have ancestry, and cousinship, 
and can only be arranged in a true system when we arrange them 
physiologically.” 
Following in the same line of instruction as above, from a 
different author — and with but little repetition — we copy this :— 
“The indoor culture of plants is intimately connected with the 
sanitary condition of our dwellings. The oxygen of the atmos- 
phere is indispensable to respiration of animals. It purifies the 
blood, affords them internal heat, and united with certain elements, 
is expired in the form of carbonic acid gas,—a compound of oxy- 
gen and carbon. This gas which is deleterious to animal life, 
constitutes the main nourishment of plants, which absorb it, appro- 
priate its carbon, and restore its oxygen to the atmosphere, again 
to be breathed in purity by men and animals. It is true that pure 
air is necessary alike to the life of plants and animals; but the 
amount of oxygen absorbed by the former is by no means equal 
to that which they restore, and thus through their agency the at- 
mosphere is kept in healthy equilibrium. 
“It is only during the day, and under the influence of light, 
however, that carbonic acid is employed for the nutrition of plants. 
That which they absorb in the night is returned to the atmosphere 
with the water which is constantly evaporating from the surface of 
