4 lo Leaves and their Functions . [J une, 
earth to the air and from the air to the earth. True, it 
sometimes tries to carry too large a load in response to the 
efficient collecting power of the leaves. They gather it in 
faster than the trunk can carry it away, and it is burst. 
We say the tree is struck with lightning ; but it has often 
been struck before, but this time it was overloaded and 
crushed. Trees are natural lightning-rods, more efficient 
than all the artificial ones that have ever been invented. 
In the next place we may contemplate the leaf as an 
organiser of organic matter. It is here that it has performed 
its most efficient and important service for man. Through 
its agency every particle of both vegetable and animal 
organism has been either direcftly or indirectly built up. 
Every plant, tree, and shrub has been direcftly built up 
through the labour of the leaf. And even long before the 
present order of things existed the leaf was at work : through 
its labours vast beds of vegetable matter were laid away far 
back in the carboniferous ages, which by heat and pressure 
have become coal, forming vast storehouses of excellent 
fuel. And still farther back, in times when Silurian seas 
washed the shores of limited bodies of land, the leaf was 
at earnest, ceaseless toil. Thus we owe to the leaf not 
only what makes life pleasant, but our food and raiment and 
fuel, without which life would be impossible. Without the 
leaf as an organiser the earth would sink back into a life- 
less, pulseless waste. 
Lastly, we may consider the leaf as a chemical agent , with- 
drawing and consolidating various poisonous gases, which if 
left in the air would render it unfit to sustain life, and thus 
convert the earth into one vast charnel-house of the dead. 
The air contains i-25ooth of its own bulk of carbonic acid, 
consisting of two equivalents of oxygen and one of carbon. 
This gas is a deadly foe to animal life, and if permitted to 
accumulate in the air would soon render it unfit to sustain 
life. And yet there are certain processes constantly going 
on that tend to augment the proportion of this gas in the 
atmosphere. Every breath of every human being and every 
living animal, and every bit of fuel that is consumed, and 
every particle of vegetable matter that decays, and every 
volcano that sends forth its deadly fumes, are adding to the 
quantity of this gas in the atmosphere. By what agency, 
then, is the equilibrium maintained ? It is through the 
agency of our little friend the leaf that the work so essential 
to life and health is performed. It is constantly employed 
as an analytic chemist imbibing this poisonous gas and 
analysing it, using the carbon to build up the organic sub- 
