186 PLANT LIFE 
of modifying certain rootlets to form suckers, 
which then become attached to, and penetrate 
the tissues of, the underground parts of neigh- 
bouring plants. Although they have thus 
taken a considerable step on the road to 
parasitism, they are still not very dependent 
on the advantage they have gained. They 
retain their green leaves, and they will often 
continue to grow even when there are no suit- 
able hosts which they can attack. 
There are other species, not very distantly 
related to the foregoing, which have advanced 
much further. The Broomrapes (Orobanche) 
consist of a number of species, each parasitic 
on some kind of flowering plant. One of the 
common species grows on the roots of the 
broom, but it betrays no obvious sign of its 
existence until the flowering shaft is formed. 
The vegetative part of the plant consists of 
a small tuberous mass which is closely ad- 
herent to the root of the broom,from which, 
by means of its sucker-like roots, it derives 
the whole of its food. The bodily structure 
is simplified, and the broomrape consists of 
little more than a small underground tuber 
which produces a few specialised roots. It 
only shows itself above ground when the 
time comes for it to put forth its large and 
rapidly developing flowering shaft, on which 
are borne the reddish flowers and small 
brownish-yellow leaves. Its tiny seeds, 
like those of- some other parasites, are re- 
markable in that they do not even begin 
