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 peg-like 
protuberances which become firmly embedded 
inthe 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 
