160 



Liver Eot in North Wales, 1920-21. [May, 



of any kind, survival was prolonged. In quite a number 

 of cases such protection enabled up to 30 per cent, of the snail 

 population to survive right through the drought, rendering such 

 land unfit for stock almost as soon as moisture returned. 



The most favourable conditions for survival prevailed on old 

 grass land on heavy soils which had been trodden into deep 

 holes by horses and cattle during the winter and spring, and 

 which dried into a series of miniature ridges, alternating with 

 holes which were frequently from 4 to 6 in. in depth, and re- 

 tained the form of the hoof, thus forming more or less over- 

 hanging and cavernlike pits. In these pits water remained for 

 a long time, while sufficient moisture was retained in many 

 instances to sustain life throughout the drought. A heavy 

 growth of coarse grasses, rushes, etc., further hindered drying 

 by affording shade from sunlight, protection from winds, and 

 retention of dew. Shaded and grass-grown ditches, especially 

 if on the north side of a bank, and land to the north side and 

 under the shade of woodlands, also afforded sufficient shelter 

 for survival in several instances. During previous work it was 

 found that the egg masses of L. truncatula dried to a hard 

 scale, but on being replaced in water, speedily resumed their 

 original form. It was further noted that even after prolonged 

 drought large numbers of young snails re-appeared after the 

 return of moisture (even. in ditches, etc., that had remained 

 dry for as long as 3 months, and w 7 here all snails had died). 

 A number of laboratory and field experiments were undertaken 

 at the time, but owing to mischance, etc., did not produce con- 

 clusive proof of hatching of ova after drying, and since then 

 time has not yet allowed of their repetition. Nevertheless, soon 

 after the return of moisture numbers of minute snails appeared 

 in many places during the autumn of 1921, so that should wet 

 conditions again prevail during the spring and summer of 1922, 

 there will be a further increase in the amount of land affected. 

 It is hoped to carry out further investigations in this 

 connection. 



Field Experiments against L. truncatula. — Owing to lack of 

 time, no experiments were undertaken until June, 1921, by 

 which time the land had become very dry and vegetation dense. 

 Nevertheless, a series of spraying trials was commenced on 

 1st June on heavy grass land, very rough and much " poached," 

 situated on the Malldraeth Marsh in Anglesey. Snails w 7 ere 

 abundant and living. Plots of l/10th and l/20th acre were 

 sprayed with copper sulphate in 1/1000, 1 per cent, and 2 per 



