PARASITIC PLANTS 257 



winds and the radicle end takes root in the soil, but 

 should the lengthening stem not meet with a suitable 

 host plant the seedling dies. Should the stem reach 

 a host plant it twines itself round the stem of the 

 latter, attaching itself firmly by means of suckers or 

 haustoria. It now loses its connection with the soil, 

 and, unless checked, extends its thread-like stems to 

 neighbouring plants, rapidly spreading in all directions 

 and drawing its food supplies wholly from the host 

 plant. Large patches may in this way be rapidly 

 overcome by the Dodder, the host plants becoming 

 strangled and exhausted. 



It may be observed that Dodder possesses no chloro- 

 plasts, and is unable to take up carbon dioxide from 

 the air like an ordinary green plant, but, as already 

 stated, draws its sustenance from the ready-made 

 products which it absorbs from the host plant by 

 means of its haustoria, or suckers. 



If it be not attacked the Dodder spreads quickly, 

 produces flowers and seeds, and the soil is re-sown. 

 Dodder may also be spread by small fragments of the 

 stems, which are veritable cuttings, and may establish 

 new centres of infestation by attaching themselves to 

 new plants. It appears also that, in some cases at 

 least, Dodder may be spread by means of little 

 tubercles, which are formed in winter, 1 although in 

 general the pest is spread by seed, and chiefly, perhaps, 

 as an impurity in agricultural seeds. An idea of the 

 rapidity with which Dodder spreads may be formed 

 from M. Marre's statement, that in three months a 

 single stem may kill all the clover or lucerne plants 

 on an area of 28 square metres (say, 30 square yards), 

 and so complete is the destruction that one would say 

 a fire had passed over the spot. 



1 E. Marre, La Lutte contre la Citscitte. 



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