84 



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 slock. The beech drops (Epiphegus") is another exam- 

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



180. The mistletoe (fhorailrndron), which grows on the brancln's of 

 lrc<-s, sends its roolx into the brandies, and only the \cssels of tlie vascular 

 s\'slem arc fused ,i( cording lo some. If this is true then it probabh- oli- 

 lains only water and salts from its host. liut the mistletoe has green leaves 

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



