PARASITIC WEEDS 9 ? 



leguminous. 1 Another British species, branched broomrape 

 (O. ramosa), is of more importance in other countries, for 

 instance in America, where it works havoc among hemp crops 

 and also attacks tomatoes. 



The parasite appears above ground as a thick fleshy stem 

 bearing a number of flowers which rapidly form seed vessels 

 containing an abundance of very small seeds, which are 

 scattered by the wind. The whole plant is dingy, usually 

 brown or purple in colour, with no leaves and no trace of 

 green colouring matter. 



Broomrape seeds can lie dormant in the soil for at least 

 ten years, probably longer. They are apparently unable to 

 germinate unless they are in the immediate neighbourhood of 

 the fine fibrous roots of their proper host, and their power of 

 lying dormant enables them to await suitable conditions with- 

 out suffering from the delay. Generally speaking, they attack 

 well-developed host plants, as if they attacked young and 

 weakly plants the hosts would be so debilitated by the drain 

 on their resources that the parasite would fail to obtain 

 sufficient food to make satisfactory growth. 



The broomrape seed germinates and puts out a small 

 radicle or root which penetrates a fine rootlet of the host and 

 soon connects itself with the conducting strand. This radicle 

 at once begins to steal food from the host, and stores it up in 

 the form of a starchy reserve food in the upper part of the 

 radicle which swells up and gradually forms a nodule on the 

 host root. This nodule increases in size and after a time a 

 number of small prominences appear on its surface, a larger 

 swelling developing just where the seed coat was at first 

 present. The small prominences grow out into roots which 

 surround the nodule closely and attack the host roots in other 

 places, thus providing several points of attachment instead of 

 only one. The larger swelling develops into a shoot, short 

 and covered with scales, which eventually elongates and grows 



1 Garman, H. (1903), Kentucky Agric. Exp. Stat. Bull., 105, p. 31, gives 

 a list of English plants attacked by Orobanche minor. 



Crepis virens Poterium sanguisorba ? 



Crithmum maritimum Trifolium arvense. 



Daucus carota pratense. 



Digitalis pur pur ea 

 Hypocharis radicata 

 Lotus corniculatus 

 Medicago lupulina 

 sativa 



rep ens. 

 strictum. 

 subterraneum. 

 striatum. 

 filiforme. 



7 



