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 



