54 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
worker, in the valuable contribution " L'Anguillule de la Tige," gives 
a list of some forty plants which are susceptible to the attacks of 
Tylenchus devastatrix. This list includes, among our principal food 
crops, Rye, Oats, Onions, and Clover, and in a less degree Barley and 
Wheat. Among flowering plants, Hyacinths, Scillas, and Galtonia 
candicans are included in the list. Narcissus is not, however, 
mentioned. Some of our commonest weeds, such as Sweet Vernal 
Grass, Meadow Soft Grass, Annual Meadow Grass, the Buttercup, 
the Daisy, and the Plantain are also liable to infection. 
In 1900 Ritzema Bos put forward the biological-strain theory, 
which, in brief, is that Tylenchus devastatrix becomes so adapted to a 
particular species of host plant after growing on it for several genera- 
tions, that it will not attack with any severity any other species. 
Further, taken from such a second species, it will not attack the original 
host with severity until after several generations have passed. For 
instance, according to him the Narcissus strain is not likely to affect 
onions with any severity, and vice versa, although the two strains are 
absolutely indistinguishable under the. microscope. In like manner, 
it has been suggested by several investigators that the root-knot eel- 
worm Heterodera radicicola may show similar biological strains with 
no apparent morphological differences. 
In conjunction with the series of inoculation experiments per- 
formed last September, to which reference has already been made, 
certain experiments were carried out to test the truth of this theory. 
Healthy bulbs were planted in sterilized soil and onion seed sown 
on the surface. The pots were watered twice with eelworm cultures 
(the eelworms being originally taken from Narcissus bulbs) at the inter- 
val of a fortnight. The eelworms had their original diet to feed upon, 
but, in contradiction to the biological-strain theory, all the seedling 
onions were attacked. Another similar experiment was made by 
sowing onion seeds in sterilized soil in pots and watering once before 
germination with water containing the Narcissus strain of eelworm. 
Six weeks after sowing, although the seed showed a moderate ger- 
minative capacity, practically none of the seedlings carried the seed 
husk at their tip, and abnormal twisting or bending was very notice- 
able. The young plants were of a lighter green colour than those in 
the control pots. The seedlings in the infected soil gradually died 
off, and on examination were found to contain Tylenchus in numbers. 
I have a photograph showing the characteristics of the diseased seed- 
lings, illustrating especially the swollen bases and deformed growth. 
Scilla nutans has also been successfully cross-inoculated with the 
Narcissus strain of Tylenchus, and a number of other crops are under 
observation. 
This phase of the subject has been treated in detail because it 
opens up a very wide field and is of great economic importance on 
account of its bearing on the rotation of crops. For instance, in parts 
of the country where bulbs are grown in rotation with agricultural 
crops, it is of little use, in attempting to control Narcissus disease, to grow 
