756 



" New Agricultural Pest. — Professor Henslow last week called attention to the si- 

 lent but dangerous progress that is making by a new agricultural pest, the clover dod- 

 der, which threatens to destroy the clover crop altogether in some places. 



" The dodders are a singular race of true parasites, inhabiting all the temperate 

 and warmer parts of the globe, distinguished by botanists into numerous species, but 

 all having the same manner of growth and multiplication. They are leafless annual 

 plants, allied to the bindweeds [Convolvulaceae], and, like them, strangling whatever 

 they lay hold of. Their flowers, which are small, appear in balls on the stems, spee- 

 dily form fruit, and end in producing each four seeds, about the size of a grain of mus- 

 tard, within which is coiled up an embryo plant, looking like a miniature snake. As 

 the number of flowers in each ball is, in our common species, on an average, about fif- 

 teen, it follows that every ball will furnish about sixty young plants — whence the ra- 

 pid spread of such pests may be easily understood. 



" As soon as the seed of the Dodder is ripe, it falls to the ground, and usually 

 seems to lie dormant till the succeeding year ; sometimes, however, it is said to ger- 

 minate immediately. When the spring returns, the embryo sends one end down into 

 the earth to form a root, while the other rises upwards, like a small white thread or 

 worm. At this time it is not a parasite, but seems to derive its food from the soil, like 

 ordinary plants. It cannot, however, do so long, but withers and perishes, unless it 

 touches some living branch or stem. If it succeed in doing so, it immediately seizes 

 the live stem by means of a sucker, which is protruded from the point of contact; and 

 then twining from left to right, and forming more suckers as it twines, it establishes 

 itself on its victim, and ceases to have any further connexion with the soil. From 

 that time forward it is a true parasite, feeding on the juices of the plant it has seized 

 upon. After making a few turns round the branch, and securing itself firmly in its 

 new position, it again lengthens, and catches hold of some other branch, when more 

 suckers are protruded ; and thus it goes on — branching, and twining, and sucking, 

 and branching again — until it forms that appearance which Prof. Henslow well de- 

 scribes as resembling ' fine, closely-entangled, wet catgut.' Now the dodder has a new 

 and independent seat of life wherever it has twined round a branch ; and as it is in- 

 cessantly twining and separating, and twining again, a single plant is speedily in the 

 condition of a polype — so that if it be cut into a thousand pieces, each piece will imme- 

 diately go on growing, as if nothing had happened to it. Tearing the dodder in pieces 

 then, so far from extirpating it, only multiplies the mischief, instead of an-estiug it. 



" This short statement will show that it is a formidable enemy that has thus been 

 unfortunately introduced to our fields ; and, as these things are not very nice in their 

 food, it is not impossible that the clover dodder may next take a fancy to our wheat- 

 fields, unless we can speedily put an end to its presence. It is of little use to cut it in 

 pieceg — it is of no use whatever to do so, if the fragments are left where they can catch 

 hold of anything else. 



" As it is only an annual, it would be killed if we could prevent its flowering; but 

 that is difficult, because of its hiding itself among the lower branches of plants, where 

 it cannot be seen : and a few heads of flowers will soon renew it in a succeeding year. 

 The right plan would be to dig up the clover where the dodder appears, so as to form 

 a circle considerably beyond the patch apparently formed by it, and then to burn it in 

 heaps; or, in cases where the entire field is infected by it, to sacrifice the whole crop, 

 and burn it. This may appear a violent remedy, but it is the only one likely to be ef- 

 fectual ; and even tliis will fiiil, if (which is not yet the case, but soon will be) the dod- 



