32 
INTRODUCTION. 
IV. 
indirectly, depend on whatever agency in the first instance seizes on inorganic mat- 
ter, and converts it into living substance suitable to enter into the composition of 
animal nerve and muscle. And this agency is assuredly the office of the vegetable 
kingdom, here confined in the main to Algae ; we thus sufficiently establish our 
position that the Algae are indispensable to the continuance of organic life in the 
sea. 
As being the first vegetables that prey upon dead matter, and as affording 
directly or indirectly a pasture to all water animals, the Algae are entitled to notice. 
Yet this is but one-half of the task committed to them. Equally important is the 
influence which their growth exerts on the water and on the air. The well known 
fact that plants, whilst they fix carbon in an organized form in extending their 
bodies by the growth of cells, exhale oxygen gas in a free state, is true of the 
Algae as of other vegetables. By this action they tend to keep pure the water in 
which they vegetate, and yield also a considerable portion of oxygen gas to the 
atmosphere. I have already stated that whenever land becomes flooded, or where- 
ever an extensive surface of shallow water — whether fresh or salt — is exposed to 
the air, Confervce and allied Algae quickly multiply. Every pool, every stagnant 
ditch is soon filled with their green silken threads. These threads cannot grow 
without emitting oxygen. If you examine such a pool on a sunny day, you may 
trace the beads of oxygen on the submerged threads, or see the gas collect in 
bubbles where the threads present a dense mass. It is continually passing off into 
the air while the Confervse vegetate, and this vegetation usually continues vigorous, 
one species succeeding another as it dies out, as long as the pool remains. And 
when, on the drying up of the land, the Confervas die, their bodies, which are 
scarcely more than membranous skins filled with fluid, shrivel up, and are either 
carried away by the wind or form a papery film over the exposed surface of the 
ground. In neither case do they breed noxious airs by their decomposition. All 
their life long they have conferred a positive benefit on the atmosphere, and at 
their death they at least do no injury. The amount of benefit derived from each 
individual is indeed minute, but the aggregate is vast when we take into account 
the many extensive surfaces of water dispersed over the world, which are thus kept 
pure and made subservient to a healthy state of the atmosphere. It is not only 
vast, but it is worthy of Him who has appointed to even the meanest of His 
creatures something to do for the good of His creation. 
These general uses of the Algae, apparent as they are on a slight reflection, are 
apt to be overlooked by the utilitarian querist, who will see no use in anything 
which does not directly minister to his own wants, and who often judges of the 
use of a material by the dollars and cents which it brings to his pocket. 
It would be in vain to adduce to him the indirect benefit derived to the rest of 
creation through the lower animals which the Algae supply with food ; for probably 
he would turn round with the further demand, u what is the use of feeding all 
these animals ?” And he might think, too, that the amount of oxygen in the air 
was quite enough to last out at least his time, without such constant renovation as 
the Algae afford, or that sufficient renovation would come from other sources had 
the Algae never been created. “ Show me,” he would say, “ how I can make money 
