YOUNGER YEARS OF A PLANT. 171 



rivers and estuaries, until the thus arrested and decom- 

 posing substances form fever-breeding swamps. When the 

 flood recedes the roots are left uncovered, and often found 

 filled with shell-fish a fact which explains the wonderful 

 tales of early travellers in the tropics, that there were 

 trees found in the East and West Indies on whose branches 

 oysters were growing. 



Other roots have no home in earth or water; they 

 must even be content to hang, all their lifetime, high and 

 dry in the air. Some, it is true, accomplish a firmer 

 settlement, late in life, as those of the screwpine of the 

 tropics, which grow not only at the foot of the tree, but 

 for a considerable height from all parts of the trunk, to 

 protect the plant against violent winds. From thence 

 they hang down into the air and furnish us with a beautiful 

 evidence of creative design in the structures of the vegeta- 

 ble world. They are, namely, at this stage of their growth, 

 provided with a kind of cup at each extremity, which 

 catches every stray drop of rain and dew, and thus en- 

 ables them both to grow themselves and to furnish nutri- 

 ment to the parent plant. In the course of time, however, 

 they reach the ground, and instantly these cups fall off, 

 as the roots now need such extraordinary assistance no 

 longer. Others spend their lives, literally, in building cas- 

 tles in the air. Almost all the orchids of the Tropics 

 use a tree, a block of wood, or a stone, merely as a 

 support on which to settle down, and over which to spread 

 their aerial roots. These, however, do not penetrate into 

 the substance; the plants have no other source of nutri- 

 ment than the vapor of the damp, heated atmosphere 



