258 Black Currant Eelworm 



imitated by a daily overhead watering with a can the rose of which 

 had large holes. 



At the termination of the experiment it was found, contrary to 

 expectation, that the buds of both series with the exception of a few 

 cases were unattacked by worm. There was some difficulty in under- 

 standing such results. It was thought probable however that two 

 factors, working either separately or conjointly, produced this compara- 

 tive immunity in the seedlings. These factors w^ere (i) the condition 

 of inactivity of the worm at the time of inoculation, and (ii) the efEect 

 of forceful descending water on worms in that state. 



In dealing with the first factor it is necessary to explain the method 

 employed for obtaining worms for bud inoculation purposes in this 

 experiment. This consisted in allowing diseased buds taken from the 

 orchard to become sufficiently dry to induce the worms to form colonies 

 in the scale leaves. In this manner they were obtained in great numbers 

 and were convenient to handle. Such worms would not be in a 

 thoroughly desiccated condition, but they would, on the other hand, 

 be incapable of becoming immediately active when immersed in 

 water. Taking this into consideration it is evident that a strong 

 force of water coming in contact with colonies of worms loosely inserted 

 in the scale leaves might carry them down to the soil before they could 

 become sufficiently active to invade the buds in their descent. Those 

 buds which became infected were, it is supposed, invaded by nema- 

 todes which had remained in the scale leaves until their activity was 

 regained or which had reascended the stem from the soil. 



The condition of the worms which thus influenced this section of 

 the experiment dealing with bud inoculation, could not in the same 

 manner have influenced that in which infection was brought about 

 through the soil. In this case the worms would be kept active through- 

 out the experiment by the moisture always present. 



It is only possible therefore to conjecture that the rapid downward 

 trend of the drops of water was sufficiently forceful to prevent the worms 

 from ascending the stems of the plants in any numbers. In this connec- 

 tion it is of interest to note the conduct of drops of water as they fall 

 upon the leafless stems of the plants. They collect at the buds, entirely 

 immerse them for a few seconds, run quickly down and round the 

 stem to the succeeding lower buds until the soil is reached. There 

 is little doubt that in this manner migrating worms resting within 

 the scale leaves in a desiccated condition, when they float readily on 

 the surface of the water, are carried to the soil. 



