PARASITIC PLANTS 



263 



OROBANCHACE^: 



The only weeds in this order are those of the genus 

 Orobanche, known as the 

 Broom-rapes, or robbers of 

 Broom, from two Greek words 

 meaning a vetch and to strangle, 

 the vetch probably being re- 

 placed by Broom, which is 

 commonly infested. The 

 Broom-rapes, of which there 

 are about one hundred species, 

 are not so harmful as Dodder, 

 but they may sometimes be 

 very troublesome, especially 

 on warm, dry, light soils. 



Broom-rapes are annual, 

 leafless, brownish root-para- 

 sites, containing no chloro- 

 phyll or green colouring 

 matter. The stems are 6 

 inches to 2 feet high, generally 

 stout and scaly, with a some- 

 what tuberous base, and occur 

 singly ; and the flowers, with 

 certain exceptions, occur in 

 lax or dense spikes. Finally, 

 the plant is attached, by 

 means of suckers or haustoria, 

 to the roots of the clover or 

 other plant on which it is 

 parasitic. It subsists on the 

 food material manufactured 

 by the host plant, and if it be very plentiful the clover 

 crop may be almost or quite ruined. 



FlG. 73. Broom-rape (Orobanche 

 minor Suit.), nat. size. 



