1906.] 



Dodder. 



333~ 



coiled spirally round the fleshy albumen, while the radicle is 

 thickened. The seeds seem to germinate best during damp 

 seasons. At a suitable temperature they will germinate in five 

 to eight days. When a seed germinates the thread-like coil 

 unwinds gradually, the radicle end taking root in the soil, the 

 remainder meanwhile lengthening and when it reaches a suit- 

 able host commencing to twine itself round the stem, to which 

 it attaches itself firmly by means of the suckers or haustoria. 

 Should the thread-like stems fail to reach a suitable host plant, 

 they die. 



The plant now extends its thread-like stems to neighbouring 

 plants, and large patches may rapidly become infested and 

 overcome, the dodder soon leaving its hold of the soil, and 

 living wholly on the host plant. On becoming firmly estab- 

 lished the dodder grows and spreads rapidly, produces flowers, 

 and if nothing be done, seeds are formed and the soil is re-sown^ 

 Small fragments of the stems, constituting veritable cuttings, 

 may suffice to establish new centres of infestation, attaching 

 themselves to fresh plants. But M. Marre states that dodder 

 may also be spread by means of little tubercles, which are 

 formed in winter.* 



As stated above, however, dodders are annual seed-producing 

 plants, and are no doubt chiefly distributed by seed included 

 amongst agricultural seeds. 



As regards the life-history and manner of growth, the various 

 species closely resemble one another. The harm done is best 

 explained by stating that dodder possesses no chloroplasts, and 

 is unable to take up carbon dioxide from the air like ordinary 

 green plants, but after leaving its hold of the soil, it depends 

 entirely for its food material on the ready-made products which 

 it absorbs from its host plant, which therefore becomes ex- 

 hausted and dies. So rapidly does the pest spread that it has 

 been stated that in three months a single stem may kill all the 

 clover or lucerne plants on an area of twenty-eight square 

 metres (thirty square yards nearly), and so complete is the 

 destruction that one would say a fire had passed over the spot. 

 Infested plants may be said to present the appearance of being 

 wound about with reddish or yellow threads. 



* E. Marre, La Lntte c out re la C 11 scute. 



