8 4 



PHYSIOLOGY. 



sitic on clover, and a great variety of other plants. There is food enough 

 in the seed for the young plant to take root and develop a slender stem until 

 it takes hold of its host. It then twines around the stem of its host send- 

 ing wedge-shaped haustoria into the stem to obtain food. The part then 

 in connection with the ground dies. 



The haustoria of the dodder form a complete junction with the vascular 

 bundles of its host so that through the vessels water and salts are obtained, 

 while through the junction of sieve tubes the elaborated organic food is 



obtained. The union of the dodder with its host is like that between a 

 graft and the graft stock. The beech drops (Epiphegus) is another exam- 

 ple of a parasitic seed plant. It is parasitic on the roots of the beech. 



180. The mistletoe (Phoradendron), which grows on the branches of 

 trees, sends its roots into the branches, and only the vessels of the vascular 

 system are fused according to some. If this is true then it probably ob- 

 tains only water and salts from its host. But the mistletoe has green leaves 

 and is thus able to assimilate carbon dioxide and manufacture its own 



