REMEDIAL MEASURES 47 



that Persicaria or Redshank (Polygomtm Persicarid) was 

 completely killed by a 4 per cent solution of copper 

 sulphate, 100 gallons per acre sprayed on clover and 

 grass seeds sown in May, the clover and grass being 

 uninjured. 



The solutions are partially effective on Docks, Black 

 Bindweed (Polygonum Convolvulus), Dandelion, Perennial 

 Sow Thistle (Sonchus arvensis), Poppy (see p. 55), 

 Spurrey (see p. 74), Groundsel, and Corn Cockle, and 

 while these are not completely destroyed, seeding is 

 generally prevented. Spraying with solutions of the 

 strengths mentioned above has also no permanent effect 

 on Cornflower (Centaurea Cyanus), Bindweeds (Convol- 

 vulus sp.), Creeping Thistle (Cnicus arvensis), species 

 of Anthemis and Matricaria, Couch and Horse-tails. 

 Although the leaves of these weeds are turned brown 

 and killed in patches the plants are able to continue 

 growth, and ultimately produce flowers and ripe seeds. 



Species of Chenopodium, Spurges (Euphorbia sp.), 

 Fumitory, and Sisymbrium Thaliana are protected by 

 the glaucous bloom on the leaves, and spraying, even 

 with very much stronger solutions than those men- 

 tioned, has little or no effect upon them. Knot-grass 

 (Polygonum Aviculare] and Small Toadflax (Linaria minor) 

 also resist these solutions. 



As spraying is chiefly used against weeds growing 

 among ordinary farm crops, it is important to deter- 

 mine to what extent the latter are injured by copper 

 and iron sulphate solutions. In the strengths given 

 above it has been found that cereals are not perman- 

 ently injured by them. The tips of the leaves are 

 generally killed and sometimes portions of the flat 

 leaves also, but the growing points are effectively pro- 

 tected and continue to grow, new leaves are unfolded, 

 and the crop does not suffer. 



