FLOWERING PARASITES 183 



we often associate mentally with a parasitic 

 habit, but it has nevertheless undergone 

 considerable modification in its root structure, 

 whilst there is little in its stems and leaves, 

 or in the internal anatomy of these organs, 

 to indicate its particular habit of life. The 

 reason lies solely in the circumstance that it 

 has in no way abandoned the functions of 

 independent photosynthesis. It only with- 

 draws water and inorganic salts from the 

 host plant which it infests, but makes no 

 demand upon it for sugars and other com- 

 plex organic food. It is mainly in respect of 

 its root system that it has become modified, 

 for the machinery requisite for continual 

 absorption of water from the wood of a living 

 tree is very different from that which is 

 adapted to discharge a similar function in 

 the soil. Branching green structures, which 

 probably represent creeping stems, traverse 

 the rind of the tree on which the mistletoe is 

 growing, and from these there grow 1 peg-like 

 protuberances which become firmly embedded 

 in the wood. These pegs are the real mistletoe 

 roots, and they are very carefully adjusted in 

 the manner of their growth to the habits of 

 the particular tree in which they occur. Their 

 rate of elongation exactly coincides with that 

 of the increase in thickness of the branch. 

 It is, of course, only this accurate adjustment 

 that renders it possible for the mistletoe to 

 flourish at all, for it is clear that the roots 

 would otherwise be unable to maintain that 



