THE WONDEES OP THE SHOEE. 181 



commonest of all, tlie delicate green Ulva, whicli yon 

 will see growing everywhere in wrinkled fan-shaped 

 sheets, as thin as the finest silver-paper. The smallest 

 bits of stone are sufficient, provided the sea-weeds 

 have hold of them ; for they have no real roots, but 

 adhere by a small disc, deriving no nourishment 

 from the rock, but only from the water. Take care, 

 meanwhile, that there be as little as possible on the 

 stone, beside the weed itself. Especially scrape off 

 any small sponges, and see that no worms have made 

 their twining tubes of sand among the weed-stems ; 

 if they have, drag them out ; for they will surely 

 die, and as surely spoil all by sulphuretted hydrogen, 

 blackness, and evil smells. 



Put your weeds into your tank, and settle them at 

 the bottom ; which last, some say, should be covered 

 with a layer of pebbles : but let the beginner leave it 

 as bare as possible ; for the pebbles only tempt cross- 

 grained annelids to crawl u.nder them, die, and spoil 

 all by decaying : whereas if the bottom of the vase 

 is bare, you can see a sickly or dead inhabitant at 

 once, and take him out (which you must do) instantly. 



