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 Alg£e are indispensable to the continuance of organic life in the 

 sea. 



As being the first vegetables that prey upon dead matter, and as afirording 

 directly or indirectly a pasture to all water animals, the Algas are entitled to notice. 

 Yet this is but one-half of the task committed to them. Equ;ally important is the 

 influence which their growth exerts on the water and on the air. The welhknown 

 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 

 Alga3 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 ofi^ into 

 the air while the Confervae 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 Conferva 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 Algas, 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, " 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 Algce afford, or that sufiicient renovation would come from other sources had 

 the Alga3 never been created. " Show me," he would say, " how I can make money 



