TRESH-WATEE ALG^E. 341 



case of those whose filaments may be some feet in length, 

 and which cannot fail to be seen, as they grow in masses of 

 considerable breadth, the filaments are so densely crowded, 

 that instead of being regarded as plants, they are looked 

 upon as some green impurity, which in Scotland goes under 

 the general name of daah. When a small portion, however, 

 of this despised slaak is taken, and laid on talc, and examined 

 by the aid of a microscope, or even a hand lens, the person 

 who thus beholds it will be filled with astonishment; he 

 will see that what he regarded as shapeless filth, is of exqui- 

 site workmanship, and worthy of the Hand by which it was 

 made ; and he may learn that what he thought worse than 

 useless, instead of polluting the waters, is one great cause 

 of their purity and wholesomeness ; that without these 

 Algee the waters would soon become so putrid and poi- 

 sonous as to spread malaria over wide districts of country, 

 and lay them desolate. 



But these are not the only purposes they serve. They 

 afford shelter to countless myriads of living creatures, espe- 

 cially infusorial animalcules, which not only enjoy life, but 

 — ^minute though they be, and unseen by man, — perform 

 wonderful functions for his benefit. They are found most 

 abundantly in all stagnant waters : 



