250 Black Currant Eelworin 



arrived there they may, on resuming their activity, reascend the tree, 

 or proceed to a neighbouring bush, if moist conditions prevail for 

 sufficient time to enable them to travel there. 



That wind may act as a distributing factor of wider range when 

 the worms are in a quiescent condition is highly probable but difficult 

 of observation. The scale leaves of the dead buds become extremely 

 brittle in dry weather, the slightest movement being sufficient to 

 detach them from the, main body of the bud. Such leaves with the 

 attached colonies of worms adhering to them, would in this manner 

 be carried by the ■v\dnd to some considerable distance. 



Such briefly are the habits of the worms and the conditions con- 

 trolling them at the migratory period. The various stages will, however, 

 be reconsidered later and in greater detail when experimental work 

 dealing with migration is described. 



The life history of the nematodes within the bud has now been 

 outlined, and the effect of the parasites on the vegetative parts of these 

 structures follows. 



From the examination of numerous newly attacked buds it is seen 

 that the worms generally adopt one of two methods of attack. They 

 either, (i) group themselves at the bases of the scale leaves, or (ii) dis- 

 tribute themselves throughout the entire bud. 



In the first case the scale leaves are the object of attack. These 

 function as protective organs and are therefore more resistant and 

 less succulent than the true leaves. There is however at their extreme 

 bases a ring, limited in area, of very succulent tissue. Here the worms 

 collect, and by the constant perforation of the tissue in this region, 

 cause the vessels which are of vital importance to the life of the leaf 

 to collapse. The decay of the whole structure, thus cut off from its 

 source of supply, rapidly ensues, and a condition of decay, in which 

 the worms live and multiply, is set up. 



The latter case, in which distribution throughout the bud occurs, 

 is one of peculiar interest, in that it throws light on the habits of the 

 worms in relation to the bud mechanism. It has been suggested in 

 a previous paper ^ that the oil-glands of the black currant bud are to 

 a certain extent responsible for the attack of Eriophyes ribis. The 

 following observation tends to confirm that theory. 



The glands in question are epidermal outgrowths, and cover at 

 close intervals the outer surfaces of the scale and true leaves of the 

 buds of Ribes nigrum. They are considerably raised above the surfaces 



^ Journal of Agricultu7-al Science, Vol. VI, VsiTtu, p. 121. 



