174 
Trap-plants for Eehoorms. 
into the error of regarding it as an Acarus, or mite. Specimens of 
beetroot sent to him from Silesia, where the crop had been severely 
attacked, enabled Schacht to acquire a more correct view of the 
character of the parasite. After his death, however, the pest, the 
possibly serious nature of the ravages of which he had clearly fore- 
seen, appears to have fallen out of notice. Such was the state of 
affairs when, in 1871, A. Schmidt, in Zeitschrift fiir Ruhenzucker- 
industrie, directed public attention for the second time to this 
minute creature, and bestowed upon it the name of Heterodera 
Schachtii. 
In subsequent years the “ Ruben-nematode ” (or beetroot thread- 
worm), as it came to be called in Germany, attracted the attention 
of Leuckart, Schneider, and other specialists, but it was not till 
1881 that Julius Kiihn, in his work Untersuchungen iiber die 
Ursache der Ruhenmiidigkeit (Inquiries into the Cause of Beetroot 
Sickness), arrested the public notice by his account of the steadily 
growing losses to which chenopodiaceous plants were subjected 
through the activity of this pest. He gave a long list of the plants 
which harbour the eelworm, and then suggested the ingenious plan 
of combating its ravages by resorting to the use of what in France 
are termed plantes-pieges, which may perhaps be rendered in English 
as “ trap-plants ” ; that is, plants cultivated with the express object 
of attracting the eelworms, or decoying them away from the soil 
which they infest. Recent researches have confirmed the belief that 
Heterodera Schachtii is capable of finding a congenial environment 
in numerous species of plants. That, as a recognised pest of beet 
and mangel, it should further extend its ravages to spinach, which, 
like them, is also a chenopodiaceous plant, is what might fairly have 
been anticipated. But it is found to equally attack the cereals, 
especially wheat and oats, and it marks as its victims a whole series 
of cruciferous plants, such as the turnip, swede, rape, cabbage, kale, 
kohl-rabi, radish, mustard, and cress. 
In his instructive volume, Zoologie fiir Landwirte, published in 
Mai’ch 1892, Dr. J. Ritzema Bos states that as a means of preven- 
tion Kiihn (referred to in the preceding paragraph) recommends 
the employment of “ decoy-plants.” On worn-out beet ground 
he sows rapidly growing plants of a character that the eelworms 
readily infest. The plants are weeded out after the parasites have 
gone into them, but before the creatures are fully grown, or have 
again left the roots. The “decoy-plants” must be sown very thickly, 
so as to get as large a quantity of rootlets as possible in the soil. 
After these plants have been pulled up, a second set of “ decoy- 
plants ” must be grown, as all the eelworms iir tlie soil will certainly 
not have migrated into the first lot of “ catch-plants ” ; and it is even 
expedient to have a third growth. 
As seen in the beet or mangel field, the symptoms of eelworm ; 
disease are fairly characteristic, for the leaves of the plant gradu- 
ally change their bright green colour to a sickly yellow at about the 
beginning of July, or later, and ultimately die. An examination of 
the root shows this organ to be atrophied to such an extent that it 
