rOPULAR BOTANY. 459 
Those who have not visited primeval forests can form no idea of the 
beauty and the magnificence of such an appearance. In the forests of 
the tropics we frequently find trees of the greatest age and the most 
gigantic forms covered with those parasites from the bottom to the point. 
They generally belong to the tribes of ferns, lycopodia, bananas, 
orchids, &c. Such an old tree represents somewhat a botanical garden, 
where a botanist can easily spend a month or more in order to make his 
studies and collections. The most interesting among these parasites are 
the orchids, particularly remarkable -for the shape of their flowers, the 
brightness and great contrast of their colours, &c, for which reason they 
are now so frequently cultivated in one hothouses. The parasites are 
used to live at the expense of the moisture of the atmosphere. We now 
arrive at that class of plants which commonly grow on mouldering 
wood, on stones, rocks, &c, namely, the mosses, ferns and lichens, and 
by illustrating their habits we shall find that their functions in natural 
economy are of much higher importance than would be generally sup- 
posed. These plants may be regarded as the true pioneers of vegeta- 
tion. It has already been stated that the seeds of these families are so 
very light and dust-like, that they are taken up by the wind in large 
quantities and carried away to great distances, and frequently reach 
stones, rocks, and even distant barren islands, where they often germi- 
nate and grow, supported by the moisture of the atmosphere.. When in 
course of time these plants or parcels of them die and decay, a small 
layer of humus will be produced, in which the second generation, how- 
ever, will grow and prosper more rapidly. By this continued change 
of growth and decay such an increased layer of humus is produced — 
though often not till after the expiration of centuries — that larger plants 
and even the largest trees can grow and prosper in it. If we had the 
means of tracing back to its origin the history of many an island, espe- 
ciaPy of coral-reefs, we should in all probability become convinced that 
vegetation on them began and continued in this very manner. 
Among all the different functions of vegetables none are more interest- 
ing and of higher importance in regard to our own existence and health, 
than the manner in which these are instrumental in purifying the air by 
decomposing the poisonous carbonic acid gas of the atmosphere, and 
reproducing therefrom the necessary quantity of oxygen gas. 
Although the explanation of this process is somewhat circumstantial 
and the comprehension of it requires some knowledge of chemistry, I 
will endeavour to the best of my abilities to illustrate this process in the 
most popular way. 
+■ In order to reach this my aim I am obliged to start with the explana- 
tion of many other facts, connected with the phenomenon alluded to. 
We are all familiar with the fact, that no being that breathes through lungs 
is able to live for even a short time without inhaling atmospheric air. 
Beside, that by the condensation of this air the animal heat is produced 
