INTRODUCTION. xliii 



and inquire what are the direct uses of Alga in the general 

 economy of nature. On land it is only necessary to glance 

 around us to perceive that the animal kingdom could not 

 exist without the vegetable; "beasts of the forest and 

 fowls of the air," and countless myriads of the insect tribe ; 

 man himself; all depend more or less on vegetables for 

 their food and clothing. The sea too has its hordes, at 

 least as numerous as those of the land, to which the Alga 

 afford food and shelter, and on whose existence, con- 

 temptible as many of them seem, depends in a greater or 

 less degree the preservation of every scale of life in the 

 sea. Many of these little animals are so minute, that at first 

 sight it would seem a matter of very little consequence to 

 us (for when we speak of " uses," the words " to man " are 

 too generally understood) whether they should starve or not. 

 But vyhen it is remembered that the principal food of the 

 whale consists of a minute jelly-fish, which is scarcely more 

 than an animal sack moving by contraction, and that by far 

 the greater part of the fishes important as articles of food 

 to man depend on minute marine animals for support, a 

 different estimate will be formed of the importance of the 

 lower links in the chain of creation to the whole, and we 

 shall come to the conclusion that there is such a mutual 

 dependance between one living creature and another, that 

 none but the All-wise can dare to determine whether one, 

 the most minute, can be spared without endangering the 

 destruction of all. The Algce, therefore, by supporting the 

 base, support the structure. But besides this, another 

 important function is unquestionably performed by their 

 growth tending to keep pure the waters of the sea, and of 

 lakes, and thus to preserve a healthful atmosphere. Like 

 other plants they discharge a large quantity of oxygen. 



Tf these be some of the direct uses of Alga in the economy 

 of nature, their value to man, whether in agriculture, in the 



